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i40e_main.c

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  • intel_lrc.c 77.25 KiB
    /*
     * Copyright © 2014 Intel Corporation
     *
     * Permission is hereby granted, free of charge, to any person obtaining a
     * copy of this software and associated documentation files (the "Software"),
     * to deal in the Software without restriction, including without limitation
     * the rights to use, copy, modify, merge, publish, distribute, sublicense,
     * and/or sell copies of the Software, and to permit persons to whom the
     * Software is furnished to do so, subject to the following conditions:
     *
     * The above copyright notice and this permission notice (including the next
     * paragraph) shall be included in all copies or substantial portions of the
     * Software.
     *
     * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
     * IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
     * FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT.  IN NO EVENT SHALL
     * THE AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
     * LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING
     * FROM, OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS
     * IN THE SOFTWARE.
     *
     * Authors:
     *    Ben Widawsky <ben@bwidawsk.net>
     *    Michel Thierry <michel.thierry@intel.com>
     *    Thomas Daniel <thomas.daniel@intel.com>
     *    Oscar Mateo <oscar.mateo@intel.com>
     *
     */
    
    /**
     * DOC: Logical Rings, Logical Ring Contexts and Execlists
     *
     * Motivation:
     * GEN8 brings an expansion of the HW contexts: "Logical Ring Contexts".
     * These expanded contexts enable a number of new abilities, especially
     * "Execlists" (also implemented in this file).
     *
     * One of the main differences with the legacy HW contexts is that logical
     * ring contexts incorporate many more things to the context's state, like
     * PDPs or ringbuffer control registers:
     *
     * The reason why PDPs are included in the context is straightforward: as
     * PPGTTs (per-process GTTs) are actually per-context, having the PDPs
     * contained there mean you don't need to do a ppgtt->switch_mm yourself,
     * instead, the GPU will do it for you on the context switch.
     *
     * But, what about the ringbuffer control registers (head, tail, etc..)?
     * shouldn't we just need a set of those per engine command streamer? This is
     * where the name "Logical Rings" starts to make sense: by virtualizing the
     * rings, the engine cs shifts to a new "ring buffer" with every context
     * switch. When you want to submit a workload to the GPU you: A) choose your
     * context, B) find its appropriate virtualized ring, C) write commands to it
     * and then, finally, D) tell the GPU to switch to that context.
     *
     * Instead of the legacy MI_SET_CONTEXT, the way you tell the GPU to switch
     * to a contexts is via a context execution list, ergo "Execlists".
     *
     * LRC implementation:
     * Regarding the creation of contexts, we have:
     *
     * - One global default context.
     * - One local default context for each opened fd.
     * - One local extra context for each context create ioctl call.
     *
     * Now that ringbuffers belong per-context (and not per-engine, like before)
     * and that contexts are uniquely tied to a given engine (and not reusable,
     * like before) we need:
     *
     * - One ringbuffer per-engine inside each context.
     * - One backing object per-engine inside each context.
     *
     * The global default context starts its life with these new objects fully
     * allocated and populated. The local default context for each opened fd is
     * more complex, because we don't know at creation time which engine is going
     * to use them. To handle this, we have implemented a deferred creation of LR
     * contexts:
     *
     * The local context starts its life as a hollow or blank holder, that only
     * gets populated for a given engine once we receive an execbuffer. If later
     * on we receive another execbuffer ioctl for the same context but a different
     * engine, we allocate/populate a new ringbuffer and context backing object and
     * so on.
     *
     * Finally, regarding local contexts created using the ioctl call: as they are
     * only allowed with the render ring, we can allocate & populate them right
     * away (no need to defer anything, at least for now).
     *
     * Execlists implementation:
     * Execlists are the new method by which, on gen8+ hardware, workloads are
     * submitted for execution (as opposed to the legacy, ringbuffer-based, method).
     * This method works as follows:
     *
     * When a request is committed, its commands (the BB start and any leading or
     * trailing commands, like the seqno breadcrumbs) are placed in the ringbuffer
     * for the appropriate context. The tail pointer in the hardware context is not
     * updated at this time, but instead, kept by the driver in the ringbuffer
     * structure. A structure representing this request is added to a request queue
     * for the appropriate engine: this structure contains a copy of the context's
     * tail after the request was written to the ring buffer and a pointer to the
     * context itself.
     *
     * If the engine's request queue was empty before the request was added, the
     * queue is processed immediately. Otherwise the queue will be processed during
     * a context switch interrupt. In any case, elements on the queue will get sent
     * (in pairs) to the GPU's ExecLists Submit Port (ELSP, for short) with a
     * globally unique 20-bits submission ID.
     *
     * When execution of a request completes, the GPU updates the context status
     * buffer with a context complete event and generates a context switch interrupt.
     * During the interrupt handling, the driver examines the events in the buffer:
     * for each context complete event, if the announced ID matches that on the head
     * of the request queue, then that request is retired and removed from the queue.
     *
     * After processing, if any requests were retired and the queue is not empty
     * then a new execution list can be submitted. The two requests at the front of
     * the queue are next to be submitted but since a context may not occur twice in
     * an execution list, if subsequent requests have the same ID as the first then
     * the two requests must be combined. This is done simply by discarding requests
     * at the head of the queue until either only one requests is left (in which case
     * we use a NULL second context) or the first two requests have unique IDs.
     *
     * By always executing the first two requests in the queue the driver ensures
     * that the GPU is kept as busy as possible. In the case where a single context
     * completes but a second context is still executing, the request for this second
     * context will be at the head of the queue when we remove the first one. This
     * request will then be resubmitted along with a new request for a different context,
     * which will cause the hardware to continue executing the second request and queue
     * the new request (the GPU detects the condition of a context getting preempted
     * with the same context and optimizes the context switch flow by not doing
     * preemption, but just sampling the new tail pointer).
     *
     */
    #include <linux/interrupt.h>
    
    #include <drm/drmP.h>
    #include <drm/i915_drm.h>
    #include "i915_drv.h"
    #include "i915_gem_render_state.h"
    #include "intel_lrc_reg.h"
    #include "intel_mocs.h"
    
    #define RING_EXECLIST_QFULL		(1 << 0x2)
    #define RING_EXECLIST1_VALID		(1 << 0x3)
    #define RING_EXECLIST0_VALID		(1 << 0x4)
    #define RING_EXECLIST_ACTIVE_STATUS	(3 << 0xE)
    #define RING_EXECLIST1_ACTIVE		(1 << 0x11)
    #define RING_EXECLIST0_ACTIVE		(1 << 0x12)
    
    #define GEN8_CTX_STATUS_IDLE_ACTIVE	(1 << 0)
    #define GEN8_CTX_STATUS_PREEMPTED	(1 << 1)
    #define GEN8_CTX_STATUS_ELEMENT_SWITCH	(1 << 2)
    #define GEN8_CTX_STATUS_ACTIVE_IDLE	(1 << 3)
    #define GEN8_CTX_STATUS_COMPLETE	(1 << 4)
    #define GEN8_CTX_STATUS_LITE_RESTORE	(1 << 15)
    
    #define GEN8_CTX_STATUS_COMPLETED_MASK \
    	 (GEN8_CTX_STATUS_COMPLETE | GEN8_CTX_STATUS_PREEMPTED)
    
    /* Typical size of the average request (2 pipecontrols and a MI_BB) */
    #define EXECLISTS_REQUEST_SIZE 64 /* bytes */
    #define WA_TAIL_DWORDS 2
    #define WA_TAIL_BYTES (sizeof(u32) * WA_TAIL_DWORDS)
    
    static int execlists_context_deferred_alloc(struct i915_gem_context *ctx,
    					    struct intel_engine_cs *engine);
    static void execlists_init_reg_state(u32 *reg_state,
    				     struct i915_gem_context *ctx,
    				     struct intel_engine_cs *engine,
    				     struct intel_ring *ring);
    
    static inline struct i915_priolist *to_priolist(struct rb_node *rb)
    {
    	return rb_entry(rb, struct i915_priolist, node);
    }
    
    static inline int rq_prio(const struct i915_request *rq)
    {
    	return rq->priotree.priority;
    }
    
    static inline bool need_preempt(const struct intel_engine_cs *engine,
    				const struct i915_request *last,
    				int prio)
    {
    	return engine->i915->preempt_context && prio > max(rq_prio(last), 0);
    }
    
    /**
     * intel_lr_context_descriptor_update() - calculate & cache the descriptor
     * 					  descriptor for a pinned context
     * @ctx: Context to work on
     * @engine: Engine the descriptor will be used with
     *
     * The context descriptor encodes various attributes of a context,
     * including its GTT address and some flags. Because it's fairly
     * expensive to calculate, we'll just do it once and cache the result,
     * which remains valid until the context is unpinned.
     *
     * This is what a descriptor looks like, from LSB to MSB::
     *
     *      bits  0-11:    flags, GEN8_CTX_* (cached in ctx->desc_template)
     *      bits 12-31:    LRCA, GTT address of (the HWSP of) this context
     *      bits 32-52:    ctx ID, a globally unique tag
     *      bits 53-54:    mbz, reserved for use by hardware
     *      bits 55-63:    group ID, currently unused and set to 0
     *
     * Starting from Gen11, the upper dword of the descriptor has a new format:
     *
     *      bits 32-36:    reserved
     *      bits 37-47:    SW context ID
     *      bits 48:53:    engine instance
     *      bit 54:        mbz, reserved for use by hardware
     *      bits 55-60:    SW counter
     *      bits 61-63:    engine class
     *
     * engine info, SW context ID and SW counter need to form a unique number
     * (Context ID) per lrc.
     */
    static void
    intel_lr_context_descriptor_update(struct i915_gem_context *ctx,
    				   struct intel_engine_cs *engine)
    {
    	struct intel_context *ce = &ctx->engine[engine->id];
    	u64 desc;
    
    	BUILD_BUG_ON(MAX_CONTEXT_HW_ID > (BIT(GEN8_CTX_ID_WIDTH)));
    	BUILD_BUG_ON(GEN11_MAX_CONTEXT_HW_ID > (BIT(GEN11_SW_CTX_ID_WIDTH)));
    
    	desc = ctx->desc_template;				/* bits  0-11 */
    	GEM_BUG_ON(desc & GENMASK_ULL(63, 12));
    
    	desc |= i915_ggtt_offset(ce->state) + LRC_HEADER_PAGES * PAGE_SIZE;
    								/* bits 12-31 */
    	GEM_BUG_ON(desc & GENMASK_ULL(63, 32));
    
    	if (INTEL_GEN(ctx->i915) >= 11) {
    		GEM_BUG_ON(ctx->hw_id >= BIT(GEN11_SW_CTX_ID_WIDTH));
    		desc |= (u64)ctx->hw_id << GEN11_SW_CTX_ID_SHIFT;
    								/* bits 37-47 */
    
    		desc |= (u64)engine->instance << GEN11_ENGINE_INSTANCE_SHIFT;
    								/* bits 48-53 */
    
    		/* TODO: decide what to do with SW counter (bits 55-60) */
    
    		desc |= (u64)engine->class << GEN11_ENGINE_CLASS_SHIFT;
    								/* bits 61-63 */
    	} else {
    		GEM_BUG_ON(ctx->hw_id >= BIT(GEN8_CTX_ID_WIDTH));
    		desc |= (u64)ctx->hw_id << GEN8_CTX_ID_SHIFT;	/* bits 32-52 */
    	}
    
    	ce->lrc_desc = desc;
    }
    
    static struct i915_priolist *
    lookup_priolist(struct intel_engine_cs *engine,
    		struct i915_priotree *pt,
    		int prio)
    {
    	struct intel_engine_execlists * const execlists = &engine->execlists;
    	struct i915_priolist *p;
    	struct rb_node **parent, *rb;
    	bool first = true;
    
    	if (unlikely(execlists->no_priolist))
    		prio = I915_PRIORITY_NORMAL;
    
    find_priolist:
    	/* most positive priority is scheduled first, equal priorities fifo */
    	rb = NULL;
    	parent = &execlists->queue.rb_node;
    	while (*parent) {
    		rb = *parent;
    		p = to_priolist(rb);
    		if (prio > p->priority) {
    			parent = &rb->rb_left;
    		} else if (prio < p->priority) {
    			parent = &rb->rb_right;
    			first = false;
    		} else {
    			return p;
    		}
    	}
    
    	if (prio == I915_PRIORITY_NORMAL) {
    		p = &execlists->default_priolist;
    	} else {
    		p = kmem_cache_alloc(engine->i915->priorities, GFP_ATOMIC);
    		/* Convert an allocation failure to a priority bump */
    		if (unlikely(!p)) {
    			prio = I915_PRIORITY_NORMAL; /* recurses just once */
    
    			/* To maintain ordering with all rendering, after an
    			 * allocation failure we have to disable all scheduling.
    			 * Requests will then be executed in fifo, and schedule
    			 * will ensure that dependencies are emitted in fifo.
    			 * There will be still some reordering with existing
    			 * requests, so if userspace lied about their
    			 * dependencies that reordering may be visible.
    			 */
    			execlists->no_priolist = true;
    			goto find_priolist;
    		}
    	}
    
    	p->priority = prio;
    	INIT_LIST_HEAD(&p->requests);
    	rb_link_node(&p->node, rb, parent);
    	rb_insert_color(&p->node, &execlists->queue);
    
    	if (first)
    		execlists->first = &p->node;
    
    	return p;
    }
    
    static void unwind_wa_tail(struct i915_request *rq)
    {
    	rq->tail = intel_ring_wrap(rq->ring, rq->wa_tail - WA_TAIL_BYTES);
    	assert_ring_tail_valid(rq->ring, rq->tail);
    }
    
    static void __unwind_incomplete_requests(struct intel_engine_cs *engine)
    {
    	struct i915_request *rq, *rn;
    	struct i915_priolist *uninitialized_var(p);
    	int last_prio = I915_PRIORITY_INVALID;
    
    	lockdep_assert_held(&engine->timeline->lock);
    
    	list_for_each_entry_safe_reverse(rq, rn,
    					 &engine->timeline->requests,
    					 link) {
    		if (i915_request_completed(rq))
    			return;
    
    		__i915_request_unsubmit(rq);
    		unwind_wa_tail(rq);
    
    		GEM_BUG_ON(rq_prio(rq) == I915_PRIORITY_INVALID);
    		if (rq_prio(rq) != last_prio) {
    			last_prio = rq_prio(rq);
    			p = lookup_priolist(engine, &rq->priotree, last_prio);
    		}
    
    		list_add(&rq->priotree.link, &p->requests);
    	}
    }
    
    void
    execlists_unwind_incomplete_requests(struct intel_engine_execlists *execlists)
    {
    	struct intel_engine_cs *engine =
    		container_of(execlists, typeof(*engine), execlists);
    
    	spin_lock_irq(&engine->timeline->lock);
    	__unwind_incomplete_requests(engine);
    	spin_unlock_irq(&engine->timeline->lock);
    }
    
    static inline void
    execlists_context_status_change(struct i915_request *rq, unsigned long status)
    {
    	/*
    	 * Only used when GVT-g is enabled now. When GVT-g is disabled,
    	 * The compiler should eliminate this function as dead-code.
    	 */
    	if (!IS_ENABLED(CONFIG_DRM_I915_GVT))
    		return;
    
    	atomic_notifier_call_chain(&rq->engine->context_status_notifier,
    				   status, rq);
    }
    
    static inline void
    execlists_context_schedule_in(struct i915_request *rq)
    {
    	execlists_context_status_change(rq, INTEL_CONTEXT_SCHEDULE_IN);
    	intel_engine_context_in(rq->engine);
    }
    
    static inline void
    execlists_context_schedule_out(struct i915_request *rq)
    {
    	intel_engine_context_out(rq->engine);
    	execlists_context_status_change(rq, INTEL_CONTEXT_SCHEDULE_OUT);
    }
    
    static void
    execlists_update_context_pdps(struct i915_hw_ppgtt *ppgtt, u32 *reg_state)
    {
    	ASSIGN_CTX_PDP(ppgtt, reg_state, 3);
    	ASSIGN_CTX_PDP(ppgtt, reg_state, 2);
    	ASSIGN_CTX_PDP(ppgtt, reg_state, 1);
    	ASSIGN_CTX_PDP(ppgtt, reg_state, 0);
    }
    
    static u64 execlists_update_context(struct i915_request *rq)
    {
    	struct intel_context *ce = &rq->ctx->engine[rq->engine->id];
    	struct i915_hw_ppgtt *ppgtt =
    		rq->ctx->ppgtt ?: rq->i915->mm.aliasing_ppgtt;
    	u32 *reg_state = ce->lrc_reg_state;
    
    	reg_state[CTX_RING_TAIL+1] = intel_ring_set_tail(rq->ring, rq->tail);
    
    	/* True 32b PPGTT with dynamic page allocation: update PDP
    	 * registers and point the unallocated PDPs to scratch page.
    	 * PML4 is allocated during ppgtt init, so this is not needed
    	 * in 48-bit mode.
    	 */
    	if (ppgtt && !i915_vm_is_48bit(&ppgtt->base))
    		execlists_update_context_pdps(ppgtt, reg_state);
    
    	return ce->lrc_desc;
    }
    
    static inline void write_desc(struct intel_engine_execlists *execlists, u64 desc, u32 port)
    {
    	if (execlists->ctrl_reg) {
    		writel(lower_32_bits(desc), execlists->submit_reg + port * 2);
    		writel(upper_32_bits(desc), execlists->submit_reg + port * 2 + 1);
    	} else {
    		writel(upper_32_bits(desc), execlists->submit_reg);
    		writel(lower_32_bits(desc), execlists->submit_reg);
    	}
    }
    
    static void execlists_submit_ports(struct intel_engine_cs *engine)
    {
    	struct intel_engine_execlists *execlists = &engine->execlists;
    	struct execlist_port *port = execlists->port;
    	unsigned int n;
    
    	/*
    	 * ELSQ note: the submit queue is not cleared after being submitted
    	 * to the HW so we need to make sure we always clean it up. This is
    	 * currently ensured by the fact that we always write the same number
    	 * of elsq entries, keep this in mind before changing the loop below.
    	 */
    	for (n = execlists_num_ports(execlists); n--; ) {
    		struct i915_request *rq;
    		unsigned int count;
    		u64 desc;
    
    		rq = port_unpack(&port[n], &count);
    		if (rq) {
    			GEM_BUG_ON(count > !n);
    			if (!count++)
    				execlists_context_schedule_in(rq);
    			port_set(&port[n], port_pack(rq, count));
    			desc = execlists_update_context(rq);
    			GEM_DEBUG_EXEC(port[n].context_id = upper_32_bits(desc));
    
    			GEM_TRACE("%s in[%d]:  ctx=%d.%d, seqno=%x, prio=%d\n",
    				  engine->name, n,
    				  port[n].context_id, count,
    				  rq->global_seqno,
    				  rq_prio(rq));
    		} else {
    			GEM_BUG_ON(!n);
    			desc = 0;
    		}
    
    		write_desc(execlists, desc, n);
    	}
    
    	/* we need to manually load the submit queue */
    	if (execlists->ctrl_reg)
    		writel(EL_CTRL_LOAD, execlists->ctrl_reg);
    
    	execlists_clear_active(execlists, EXECLISTS_ACTIVE_HWACK);
    }
    
    static bool ctx_single_port_submission(const struct i915_gem_context *ctx)
    {
    	return (IS_ENABLED(CONFIG_DRM_I915_GVT) &&
    		i915_gem_context_force_single_submission(ctx));
    }
    
    static bool can_merge_ctx(const struct i915_gem_context *prev,
    			  const struct i915_gem_context *next)
    {
    	if (prev != next)
    		return false;
    
    	if (ctx_single_port_submission(prev))
    		return false;
    
    	return true;
    }
    
    static void port_assign(struct execlist_port *port, struct i915_request *rq)
    {
    	GEM_BUG_ON(rq == port_request(port));
    
    	if (port_isset(port))
    		i915_request_put(port_request(port));
    
    	port_set(port, port_pack(i915_request_get(rq), port_count(port)));
    }
    
    static void inject_preempt_context(struct intel_engine_cs *engine)
    {
    	struct intel_engine_execlists *execlists = &engine->execlists;
    	struct intel_context *ce =
    		&engine->i915->preempt_context->engine[engine->id];
    	unsigned int n;
    
    	GEM_BUG_ON(execlists->preempt_complete_status !=
    		   upper_32_bits(ce->lrc_desc));
    	GEM_BUG_ON((ce->lrc_reg_state[CTX_CONTEXT_CONTROL + 1] &
    		    _MASKED_BIT_ENABLE(CTX_CTRL_ENGINE_CTX_RESTORE_INHIBIT |
    				       CTX_CTRL_ENGINE_CTX_SAVE_INHIBIT)) !=
    		   _MASKED_BIT_ENABLE(CTX_CTRL_ENGINE_CTX_RESTORE_INHIBIT |
    				      CTX_CTRL_ENGINE_CTX_SAVE_INHIBIT));
    
    	/*
    	 * Switch to our empty preempt context so
    	 * the state of the GPU is known (idle).
    	 */
    	GEM_TRACE("%s\n", engine->name);
    	for (n = execlists_num_ports(execlists); --n; )
    		write_desc(execlists, 0, n);
    
    	write_desc(execlists, ce->lrc_desc, n);
    
    	/* we need to manually load the submit queue */
    	if (execlists->ctrl_reg)
    		writel(EL_CTRL_LOAD, execlists->ctrl_reg);
    
    	execlists_clear_active(&engine->execlists, EXECLISTS_ACTIVE_HWACK);
    	execlists_set_active(&engine->execlists, EXECLISTS_ACTIVE_PREEMPT);
    }
    
    static void execlists_dequeue(struct intel_engine_cs *engine)
    {
    	struct intel_engine_execlists * const execlists = &engine->execlists;
    	struct execlist_port *port = execlists->port;
    	const struct execlist_port * const last_port =
    		&execlists->port[execlists->port_mask];
    	struct i915_request *last = port_request(port);
    	struct rb_node *rb;
    	bool submit = false;
    
    	/* Hardware submission is through 2 ports. Conceptually each port
    	 * has a (RING_START, RING_HEAD, RING_TAIL) tuple. RING_START is
    	 * static for a context, and unique to each, so we only execute
    	 * requests belonging to a single context from each ring. RING_HEAD
    	 * is maintained by the CS in the context image, it marks the place
    	 * where it got up to last time, and through RING_TAIL we tell the CS
    	 * where we want to execute up to this time.
    	 *
    	 * In this list the requests are in order of execution. Consecutive
    	 * requests from the same context are adjacent in the ringbuffer. We
    	 * can combine these requests into a single RING_TAIL update:
    	 *
    	 *              RING_HEAD...req1...req2
    	 *                                    ^- RING_TAIL
    	 * since to execute req2 the CS must first execute req1.
    	 *
    	 * Our goal then is to point each port to the end of a consecutive
    	 * sequence of requests as being the most optimal (fewest wake ups
    	 * and context switches) submission.
    	 */
    
    	spin_lock_irq(&engine->timeline->lock);
    	rb = execlists->first;
    	GEM_BUG_ON(rb_first(&execlists->queue) != rb);
    
    	if (last) {
    		/*
    		 * Don't resubmit or switch until all outstanding
    		 * preemptions (lite-restore) are seen. Then we
    		 * know the next preemption status we see corresponds
    		 * to this ELSP update.
    		 */
    		GEM_BUG_ON(!execlists_is_active(execlists,
    						EXECLISTS_ACTIVE_USER));
    		GEM_BUG_ON(!port_count(&port[0]));
    		if (port_count(&port[0]) > 1)
    			goto unlock;
    
    		/*
    		 * If we write to ELSP a second time before the HW has had
    		 * a chance to respond to the previous write, we can confuse
    		 * the HW and hit "undefined behaviour". After writing to ELSP,
    		 * we must then wait until we see a context-switch event from
    		 * the HW to indicate that it has had a chance to respond.
    		 */
    		if (!execlists_is_active(execlists, EXECLISTS_ACTIVE_HWACK))
    			goto unlock;
    
    		if (need_preempt(engine, last, execlists->queue_priority)) {
    			inject_preempt_context(engine);
    			goto unlock;
    		}
    
    		/*
    		 * In theory, we could coalesce more requests onto
    		 * the second port (the first port is active, with
    		 * no preemptions pending). However, that means we
    		 * then have to deal with the possible lite-restore
    		 * of the second port (as we submit the ELSP, there
    		 * may be a context-switch) but also we may complete
    		 * the resubmission before the context-switch. Ergo,
    		 * coalescing onto the second port will cause a
    		 * preemption event, but we cannot predict whether
    		 * that will affect port[0] or port[1].
    		 *
    		 * If the second port is already active, we can wait
    		 * until the next context-switch before contemplating
    		 * new requests. The GPU will be busy and we should be
    		 * able to resubmit the new ELSP before it idles,
    		 * avoiding pipeline bubbles (momentary pauses where
    		 * the driver is unable to keep up the supply of new
    		 * work). However, we have to double check that the
    		 * priorities of the ports haven't been switch.
    		 */
    		if (port_count(&port[1]))
    			goto unlock;
    
    		/*
    		 * WaIdleLiteRestore:bdw,skl
    		 * Apply the wa NOOPs to prevent
    		 * ring:HEAD == rq:TAIL as we resubmit the
    		 * request. See gen8_emit_breadcrumb() for
    		 * where we prepare the padding after the
    		 * end of the request.
    		 */
    		last->tail = last->wa_tail;
    	}
    
    	while (rb) {
    		struct i915_priolist *p = to_priolist(rb);
    		struct i915_request *rq, *rn;
    
    		list_for_each_entry_safe(rq, rn, &p->requests, priotree.link) {
    			/*
    			 * Can we combine this request with the current port?
    			 * It has to be the same context/ringbuffer and not
    			 * have any exceptions (e.g. GVT saying never to
    			 * combine contexts).
    			 *
    			 * If we can combine the requests, we can execute both
    			 * by updating the RING_TAIL to point to the end of the
    			 * second request, and so we never need to tell the
    			 * hardware about the first.
    			 */
    			if (last && !can_merge_ctx(rq->ctx, last->ctx)) {
    				/*
    				 * If we are on the second port and cannot
    				 * combine this request with the last, then we
    				 * are done.
    				 */
    				if (port == last_port) {
    					__list_del_many(&p->requests,
    							&rq->priotree.link);
    					goto done;
    				}
    
    				/*
    				 * If GVT overrides us we only ever submit
    				 * port[0], leaving port[1] empty. Note that we
    				 * also have to be careful that we don't queue
    				 * the same context (even though a different
    				 * request) to the second port.
    				 */
    				if (ctx_single_port_submission(last->ctx) ||
    				    ctx_single_port_submission(rq->ctx)) {
    					__list_del_many(&p->requests,
    							&rq->priotree.link);
    					goto done;
    				}
    
    				GEM_BUG_ON(last->ctx == rq->ctx);
    
    				if (submit)
    					port_assign(port, last);
    				port++;
    
    				GEM_BUG_ON(port_isset(port));
    			}
    
    			INIT_LIST_HEAD(&rq->priotree.link);
    			__i915_request_submit(rq);
    			trace_i915_request_in(rq, port_index(port, execlists));
    			last = rq;
    			submit = true;
    		}
    
    		rb = rb_next(rb);
    		rb_erase(&p->node, &execlists->queue);
    		INIT_LIST_HEAD(&p->requests);
    		if (p->priority != I915_PRIORITY_NORMAL)
    			kmem_cache_free(engine->i915->priorities, p);
    	}
    done:
    	execlists->queue_priority = rb ? to_priolist(rb)->priority : INT_MIN;
    	execlists->first = rb;
    	if (submit)
    		port_assign(port, last);
    
    	/* We must always keep the beast fed if we have work piled up */
    	GEM_BUG_ON(execlists->first && !port_isset(execlists->port));
    
    unlock:
    	spin_unlock_irq(&engine->timeline->lock);
    
    	if (submit) {
    		execlists_set_active(execlists, EXECLISTS_ACTIVE_USER);
    		execlists_submit_ports(engine);
    	}
    
    	GEM_BUG_ON(port_isset(execlists->port) &&
    		   !execlists_is_active(execlists, EXECLISTS_ACTIVE_USER));
    }
    
    void
    execlists_cancel_port_requests(struct intel_engine_execlists * const execlists)
    {
    	struct execlist_port *port = execlists->port;
    	unsigned int num_ports = execlists_num_ports(execlists);
    
    	while (num_ports-- && port_isset(port)) {
    		struct i915_request *rq = port_request(port);
    
    		GEM_BUG_ON(!execlists->active);
    		intel_engine_context_out(rq->engine);
    
    		execlists_context_status_change(rq,
    						i915_request_completed(rq) ?
    						INTEL_CONTEXT_SCHEDULE_OUT :
    						INTEL_CONTEXT_SCHEDULE_PREEMPTED);
    
    		i915_request_put(rq);
    
    		memset(port, 0, sizeof(*port));
    		port++;
    	}
    
    	execlists_clear_active(execlists, EXECLISTS_ACTIVE_USER);
    }
    
    static void execlists_cancel_requests(struct intel_engine_cs *engine)
    {
    	struct intel_engine_execlists * const execlists = &engine->execlists;
    	struct i915_request *rq, *rn;
    	struct rb_node *rb;
    	unsigned long flags;
    
    	GEM_TRACE("%s\n", engine->name);
    
    	/*
    	 * Before we call engine->cancel_requests(), we should have exclusive
    	 * access to the submission state. This is arranged for us by the
    	 * caller disabling the interrupt generation, the tasklet and other
    	 * threads that may then access the same state, giving us a free hand
    	 * to reset state. However, we still need to let lockdep be aware that
    	 * we know this state may be accessed in hardirq context, so we
    	 * disable the irq around this manipulation and we want to keep
    	 * the spinlock focused on its duties and not accidentally conflate
    	 * coverage to the submission's irq state. (Similarly, although we
    	 * shouldn't need to disable irq around the manipulation of the
    	 * submission's irq state, we also wish to remind ourselves that
    	 * it is irq state.)
    	 */
    	local_irq_save(flags);
    
    	/* Cancel the requests on the HW and clear the ELSP tracker. */
    	execlists_cancel_port_requests(execlists);
    
    	spin_lock(&engine->timeline->lock);
    
    	/* Mark all executing requests as skipped. */
    	list_for_each_entry(rq, &engine->timeline->requests, link) {
    		GEM_BUG_ON(!rq->global_seqno);
    		if (!i915_request_completed(rq))
    			dma_fence_set_error(&rq->fence, -EIO);
    	}
    
    	/* Flush the queued requests to the timeline list (for retiring). */
    	rb = execlists->first;
    	while (rb) {
    		struct i915_priolist *p = to_priolist(rb);
    
    		list_for_each_entry_safe(rq, rn, &p->requests, priotree.link) {
    			INIT_LIST_HEAD(&rq->priotree.link);
    
    			dma_fence_set_error(&rq->fence, -EIO);
    			__i915_request_submit(rq);
    		}
    
    		rb = rb_next(rb);
    		rb_erase(&p->node, &execlists->queue);
    		INIT_LIST_HEAD(&p->requests);
    		if (p->priority != I915_PRIORITY_NORMAL)
    			kmem_cache_free(engine->i915->priorities, p);
    	}
    
    	/* Remaining _unready_ requests will be nop'ed when submitted */
    
    	execlists->queue_priority = INT_MIN;
    	execlists->queue = RB_ROOT;
    	execlists->first = NULL;
    	GEM_BUG_ON(port_isset(execlists->port));
    
    	spin_unlock(&engine->timeline->lock);
    
    	/*
    	 * The port is checked prior to scheduling a tasklet, but
    	 * just in case we have suspended the tasklet to do the
    	 * wedging make sure that when it wakes, it decides there
    	 * is no work to do by clearing the irq_posted bit.
    	 */
    	clear_bit(ENGINE_IRQ_EXECLIST, &engine->irq_posted);
    
    	/* Mark all CS interrupts as complete */
    	execlists->active = 0;
    
    	local_irq_restore(flags);
    }
    
    /*
     * Check the unread Context Status Buffers and manage the submission of new
     * contexts to the ELSP accordingly.
     */
    static void execlists_submission_tasklet(unsigned long data)
    {
    	struct intel_engine_cs * const engine = (struct intel_engine_cs *)data;
    	struct intel_engine_execlists * const execlists = &engine->execlists;
    	struct execlist_port * const port = execlists->port;
    	struct drm_i915_private *dev_priv = engine->i915;
    	bool fw = false;
    
    	/*
    	 * We can skip acquiring intel_runtime_pm_get() here as it was taken
    	 * on our behalf by the request (see i915_gem_mark_busy()) and it will
    	 * not be relinquished until the device is idle (see
    	 * i915_gem_idle_work_handler()). As a precaution, we make sure
    	 * that all ELSP are drained i.e. we have processed the CSB,
    	 * before allowing ourselves to idle and calling intel_runtime_pm_put().
    	 */
    	GEM_BUG_ON(!dev_priv->gt.awake);
    
    	/*
    	 * Prefer doing test_and_clear_bit() as a two stage operation to avoid
    	 * imposing the cost of a locked atomic transaction when submitting a
    	 * new request (outside of the context-switch interrupt).
    	 */
    	while (test_bit(ENGINE_IRQ_EXECLIST, &engine->irq_posted)) {
    		/* The HWSP contains a (cacheable) mirror of the CSB */
    		const u32 *buf =
    			&engine->status_page.page_addr[I915_HWS_CSB_BUF0_INDEX];
    		unsigned int head, tail;
    
    		if (unlikely(execlists->csb_use_mmio)) {
    			buf = (u32 * __force)
    				(dev_priv->regs + i915_mmio_reg_offset(RING_CONTEXT_STATUS_BUF_LO(engine, 0)));
    			execlists->csb_head = -1; /* force mmio read of CSB ptrs */
    		}
    
    		/* Clear before reading to catch new interrupts */
    		clear_bit(ENGINE_IRQ_EXECLIST, &engine->irq_posted);
    		smp_mb__after_atomic();
    
    		if (unlikely(execlists->csb_head == -1)) { /* following a reset */
    			if (!fw) {
    				intel_uncore_forcewake_get(dev_priv,
    							   execlists->fw_domains);
    				fw = true;
    			}
    
    			head = readl(dev_priv->regs + i915_mmio_reg_offset(RING_CONTEXT_STATUS_PTR(engine)));
    			tail = GEN8_CSB_WRITE_PTR(head);
    			head = GEN8_CSB_READ_PTR(head);
    			execlists->csb_head = head;
    		} else {
    			const int write_idx =
    				intel_hws_csb_write_index(dev_priv) -
    				I915_HWS_CSB_BUF0_INDEX;
    
    			head = execlists->csb_head;
    			tail = READ_ONCE(buf[write_idx]);
    		}
    		GEM_TRACE("%s cs-irq head=%d [%d%s], tail=%d [%d%s]\n",
    			  engine->name,
    			  head, GEN8_CSB_READ_PTR(readl(dev_priv->regs + i915_mmio_reg_offset(RING_CONTEXT_STATUS_PTR(engine)))), fw ? "" : "?",
    			  tail, GEN8_CSB_WRITE_PTR(readl(dev_priv->regs + i915_mmio_reg_offset(RING_CONTEXT_STATUS_PTR(engine)))), fw ? "" : "?");
    
    		while (head != tail) {
    			struct i915_request *rq;
    			unsigned int status;
    			unsigned int count;
    
    			if (++head == GEN8_CSB_ENTRIES)
    				head = 0;
    
    			/* We are flying near dragons again.
    			 *
    			 * We hold a reference to the request in execlist_port[]
    			 * but no more than that. We are operating in softirq
    			 * context and so cannot hold any mutex or sleep. That
    			 * prevents us stopping the requests we are processing
    			 * in port[] from being retired simultaneously (the
    			 * breadcrumb will be complete before we see the
    			 * context-switch). As we only hold the reference to the
    			 * request, any pointer chasing underneath the request
    			 * is subject to a potential use-after-free. Thus we
    			 * store all of the bookkeeping within port[] as
    			 * required, and avoid using unguarded pointers beneath
    			 * request itself. The same applies to the atomic
    			 * status notifier.
    			 */
    
    			status = READ_ONCE(buf[2 * head]); /* maybe mmio! */
    			GEM_TRACE("%s csb[%d]: status=0x%08x:0x%08x, active=0x%x\n",
    				  engine->name, head,
    				  status, buf[2*head + 1],
    				  execlists->active);
    
    			if (status & (GEN8_CTX_STATUS_IDLE_ACTIVE |
    				      GEN8_CTX_STATUS_PREEMPTED))
    				execlists_set_active(execlists,
    						     EXECLISTS_ACTIVE_HWACK);
    			if (status & GEN8_CTX_STATUS_ACTIVE_IDLE)
    				execlists_clear_active(execlists,
    						       EXECLISTS_ACTIVE_HWACK);
    
    			if (!(status & GEN8_CTX_STATUS_COMPLETED_MASK))
    				continue;
    
    			/* We should never get a COMPLETED | IDLE_ACTIVE! */
    			GEM_BUG_ON(status & GEN8_CTX_STATUS_IDLE_ACTIVE);
    
    			if (status & GEN8_CTX_STATUS_COMPLETE &&
    			    buf[2*head + 1] == execlists->preempt_complete_status) {
    				GEM_TRACE("%s preempt-idle\n", engine->name);
    
    				execlists_cancel_port_requests(execlists);
    				execlists_unwind_incomplete_requests(execlists);
    
    				GEM_BUG_ON(!execlists_is_active(execlists,
    								EXECLISTS_ACTIVE_PREEMPT));
    				execlists_clear_active(execlists,
    						       EXECLISTS_ACTIVE_PREEMPT);
    				continue;
    			}
    
    			if (status & GEN8_CTX_STATUS_PREEMPTED &&
    			    execlists_is_active(execlists,
    						EXECLISTS_ACTIVE_PREEMPT))
    				continue;
    
    			GEM_BUG_ON(!execlists_is_active(execlists,
    							EXECLISTS_ACTIVE_USER));
    
    			rq = port_unpack(port, &count);
    			GEM_TRACE("%s out[0]: ctx=%d.%d, seqno=%x, prio=%d\n",
    				  engine->name,
    				  port->context_id, count,
    				  rq ? rq->global_seqno : 0,
    				  rq ? rq_prio(rq) : 0);
    
    			/* Check the context/desc id for this event matches */
    			GEM_DEBUG_BUG_ON(buf[2 * head + 1] != port->context_id);
    
    			GEM_BUG_ON(count == 0);
    			if (--count == 0) {
    				GEM_BUG_ON(status & GEN8_CTX_STATUS_PREEMPTED);
    				GEM_BUG_ON(port_isset(&port[1]) &&
    					   !(status & GEN8_CTX_STATUS_ELEMENT_SWITCH));
    				GEM_BUG_ON(!i915_request_completed(rq));
    				execlists_context_schedule_out(rq);
    				trace_i915_request_out(rq);
    				i915_request_put(rq);
    
    				GEM_TRACE("%s completed ctx=%d\n",
    					  engine->name, port->context_id);
    
    				execlists_port_complete(execlists, port);
    			} else {
    				port_set(port, port_pack(rq, count));
    			}
    
    			/* After the final element, the hw should be idle */
    			GEM_BUG_ON(port_count(port) == 0 &&
    				   !(status & GEN8_CTX_STATUS_ACTIVE_IDLE));
    			if (port_count(port) == 0)
    				execlists_clear_active(execlists,
    						       EXECLISTS_ACTIVE_USER);
    		}
    
    		if (head != execlists->csb_head) {
    			execlists->csb_head = head;
    			writel(_MASKED_FIELD(GEN8_CSB_READ_PTR_MASK, head << 8),
    			       dev_priv->regs + i915_mmio_reg_offset(RING_CONTEXT_STATUS_PTR(engine)));
    		}
    	}
    
    	if (!execlists_is_active(execlists, EXECLISTS_ACTIVE_PREEMPT))
    		execlists_dequeue(engine);
    
    	if (fw)
    		intel_uncore_forcewake_put(dev_priv, execlists->fw_domains);
    
    	/* If the engine is now idle, so should be the flag; and vice versa. */
    	GEM_BUG_ON(execlists_is_active(&engine->execlists,
    				       EXECLISTS_ACTIVE_USER) ==
    		   !port_isset(engine->execlists.port));
    }
    
    static void queue_request(struct intel_engine_cs *engine,
    			  struct i915_priotree *pt,
    			  int prio)
    {
    	list_add_tail(&pt->link, &lookup_priolist(engine, pt, prio)->requests);
    }
    
    static void submit_queue(struct intel_engine_cs *engine, int prio)
    {
    	if (prio > engine->execlists.queue_priority) {
    		engine->execlists.queue_priority = prio;
    		tasklet_hi_schedule(&engine->execlists.tasklet);
    	}
    }
    
    static void execlists_submit_request(struct i915_request *request)
    {
    	struct intel_engine_cs *engine = request->engine;
    	unsigned long flags;
    
    	/* Will be called from irq-context when using foreign fences. */
    	spin_lock_irqsave(&engine->timeline->lock, flags);
    
    	queue_request(engine, &request->priotree, rq_prio(request));
    	submit_queue(engine, rq_prio(request));
    
    	GEM_BUG_ON(!engine->execlists.first);
    	GEM_BUG_ON(list_empty(&request->priotree.link));
    
    	spin_unlock_irqrestore(&engine->timeline->lock, flags);
    }
    
    static struct i915_request *pt_to_request(struct i915_priotree *pt)
    {
    	return container_of(pt, struct i915_request, priotree);
    }
    
    static struct intel_engine_cs *
    pt_lock_engine(struct i915_priotree *pt, struct intel_engine_cs *locked)
    {
    	struct intel_engine_cs *engine = pt_to_request(pt)->engine;
    
    	GEM_BUG_ON(!locked);
    
    	if (engine != locked) {
    		spin_unlock(&locked->timeline->lock);
    		spin_lock(&engine->timeline->lock);
    	}
    
    	return engine;
    }
    
    static void execlists_schedule(struct i915_request *request, int prio)
    {
    	struct intel_engine_cs *engine;
    	struct i915_dependency *dep, *p;
    	struct i915_dependency stack;
    	LIST_HEAD(dfs);
    
    	GEM_BUG_ON(prio == I915_PRIORITY_INVALID);
    
    	if (i915_request_completed(request))
    		return;
    
    	if (prio <= READ_ONCE(request->priotree.priority))
    		return;
    
    	/* Need BKL in order to use the temporary link inside i915_dependency */
    	lockdep_assert_held(&request->i915->drm.struct_mutex);
    
    	stack.signaler = &request->priotree;
    	list_add(&stack.dfs_link, &dfs);
    
    	/*
    	 * Recursively bump all dependent priorities to match the new request.
    	 *
    	 * A naive approach would be to use recursion:
    	 * static void update_priorities(struct i915_priotree *pt, prio) {
    	 *	list_for_each_entry(dep, &pt->signalers_list, signal_link)
    	 *		update_priorities(dep->signal, prio)
    	 *	queue_request(pt);
    	 * }
    	 * but that may have unlimited recursion depth and so runs a very
    	 * real risk of overunning the kernel stack. Instead, we build
    	 * a flat list of all dependencies starting with the current request.
    	 * As we walk the list of dependencies, we add all of its dependencies
    	 * to the end of the list (this may include an already visited
    	 * request) and continue to walk onwards onto the new dependencies. The
    	 * end result is a topological list of requests in reverse order, the
    	 * last element in the list is the request we must execute first.
    	 */
    	list_for_each_entry(dep, &dfs, dfs_link) {
    		struct i915_priotree *pt = dep->signaler;
    
    		/*
    		 * Within an engine, there can be no cycle, but we may
    		 * refer to the same dependency chain multiple times
    		 * (redundant dependencies are not eliminated) and across
    		 * engines.
    		 */
    		list_for_each_entry(p, &pt->signalers_list, signal_link) {
    			GEM_BUG_ON(p == dep); /* no cycles! */
    
    			if (i915_priotree_signaled(p->signaler))
    				continue;
    
    			GEM_BUG_ON(p->signaler->priority < pt->priority);
    			if (prio > READ_ONCE(p->signaler->priority))
    				list_move_tail(&p->dfs_link, &dfs);
    		}
    	}
    
    	/*
    	 * If we didn't need to bump any existing priorities, and we haven't
    	 * yet submitted this request (i.e. there is no potential race with
    	 * execlists_submit_request()), we can set our own priority and skip
    	 * acquiring the engine locks.
    	 */
    	if (request->priotree.priority == I915_PRIORITY_INVALID) {
    		GEM_BUG_ON(!list_empty(&request->priotree.link));
    		request->priotree.priority = prio;
    		if (stack.dfs_link.next == stack.dfs_link.prev)
    			return;
    		__list_del_entry(&stack.dfs_link);
    	}
    
    	engine = request->engine;
    	spin_lock_irq(&engine->timeline->lock);
    
    	/* Fifo and depth-first replacement ensure our deps execute before us */
    	list_for_each_entry_safe_reverse(dep, p, &dfs, dfs_link) {
    		struct i915_priotree *pt = dep->signaler;
    
    		INIT_LIST_HEAD(&dep->dfs_link);
    
    		engine = pt_lock_engine(pt, engine);
    
    		if (prio <= pt->priority)
    			continue;
    
    		pt->priority = prio;
    		if (!list_empty(&pt->link)) {
    			__list_del_entry(&pt->link);
    			queue_request(engine, pt, prio);
    		}
    		submit_queue(engine, prio);
    	}
    
    	spin_unlock_irq(&engine->timeline->lock);
    }
    
    static int __context_pin(struct i915_gem_context *ctx, struct i915_vma *vma)
    {
    	unsigned int flags;
    	int err;
    
    	/*
    	 * Clear this page out of any CPU caches for coherent swap-in/out.
    	 * We only want to do this on the first bind so that we do not stall
    	 * on an active context (which by nature is already on the GPU).
    	 */
    	if (!(vma->flags & I915_VMA_GLOBAL_BIND)) {
    		err = i915_gem_object_set_to_gtt_domain(vma->obj, true);
    		if (err)
    			return err;
    	}
    
    	flags = PIN_GLOBAL | PIN_HIGH;
    	if (ctx->ggtt_offset_bias)
    		flags |= PIN_OFFSET_BIAS | ctx->ggtt_offset_bias;
    
    	return i915_vma_pin(vma, 0, GEN8_LR_CONTEXT_ALIGN, flags);
    }
    
    static struct intel_ring *
    execlists_context_pin(struct intel_engine_cs *engine,
    		      struct i915_gem_context *ctx)
    {
    	struct intel_context *ce = &ctx->engine[engine->id];
    	void *vaddr;
    	int ret;
    
    	lockdep_assert_held(&ctx->i915->drm.struct_mutex);
    
    	if (likely(ce->pin_count++))
    		goto out;
    	GEM_BUG_ON(!ce->pin_count); /* no overflow please! */
    
    	ret = execlists_context_deferred_alloc(ctx, engine);
    	if (ret)
    		goto err;
    	GEM_BUG_ON(!ce->state);
    
    	ret = __context_pin(ctx, ce->state);
    	if (ret)
    		goto err;
    
    	vaddr = i915_gem_object_pin_map(ce->state->obj, I915_MAP_WB);
    	if (IS_ERR(vaddr)) {
    		ret = PTR_ERR(vaddr);
    		goto unpin_vma;
    	}
    
    	ret = intel_ring_pin(ce->ring, ctx->i915, ctx->ggtt_offset_bias);
    	if (ret)
    		goto unpin_map;
    
    	intel_lr_context_descriptor_update(ctx, engine);
    
    	ce->lrc_reg_state = vaddr + LRC_STATE_PN * PAGE_SIZE;
    	ce->lrc_reg_state[CTX_RING_BUFFER_START+1] =
    		i915_ggtt_offset(ce->ring->vma);
    
    	ce->state->obj->pin_global++;
    	i915_gem_context_get(ctx);
    out:
    	return ce->ring;
    
    unpin_map:
    	i915_gem_object_unpin_map(ce->state->obj);
    unpin_vma:
    	__i915_vma_unpin(ce->state);
    err:
    	ce->pin_count = 0;
    	return ERR_PTR(ret);
    }
    
    static void execlists_context_unpin(struct intel_engine_cs *engine,
    				    struct i915_gem_context *ctx)
    {
    	struct intel_context *ce = &ctx->engine[engine->id];
    
    	lockdep_assert_held(&ctx->i915->drm.struct_mutex);
    	GEM_BUG_ON(ce->pin_count == 0);
    
    	if (--ce->pin_count)
    		return;
    
    	intel_ring_unpin(ce->ring);
    
    	ce->state->obj->pin_global--;
    	i915_gem_object_unpin_map(ce->state->obj);
    	i915_vma_unpin(ce->state);
    
    	i915_gem_context_put(ctx);
    }
    
    static int execlists_request_alloc(struct i915_request *request)
    {
    	struct intel_engine_cs *engine = request->engine;
    	struct intel_context *ce = &request->ctx->engine[engine->id];
    	int ret;
    
    	GEM_BUG_ON(!ce->pin_count);
    
    	/* Flush enough space to reduce the likelihood of waiting after
    	 * we start building the request - in which case we will just
    	 * have to repeat work.
    	 */
    	request->reserved_space += EXECLISTS_REQUEST_SIZE;
    
    	ret = intel_ring_wait_for_space(request->ring, request->reserved_space);
    	if (ret)
    		return ret;
    
    	/* Note that after this point, we have committed to using
    	 * this request as it is being used to both track the
    	 * state of engine initialisation and liveness of the
    	 * golden renderstate above. Think twice before you try
    	 * to cancel/unwind this request now.
    	 */
    
    	request->reserved_space -= EXECLISTS_REQUEST_SIZE;
    	return 0;
    }
    
    /*
     * In this WA we need to set GEN8_L3SQCREG4[21:21] and reset it after
     * PIPE_CONTROL instruction. This is required for the flush to happen correctly
     * but there is a slight complication as this is applied in WA batch where the
     * values are only initialized once so we cannot take register value at the
     * beginning and reuse it further; hence we save its value to memory, upload a
     * constant value with bit21 set and then we restore it back with the saved value.
     * To simplify the WA, a constant value is formed by using the default value
     * of this register. This shouldn't be a problem because we are only modifying
     * it for a short period and this batch in non-premptible. We can ofcourse
     * use additional instructions that read the actual value of the register
     * at that time and set our bit of interest but it makes the WA complicated.
     *
     * This WA is also required for Gen9 so extracting as a function avoids
     * code duplication.
     */
    static u32 *
    gen8_emit_flush_coherentl3_wa(struct intel_engine_cs *engine, u32 *batch)
    {
    	*batch++ = MI_STORE_REGISTER_MEM_GEN8 | MI_SRM_LRM_GLOBAL_GTT;
    	*batch++ = i915_mmio_reg_offset(GEN8_L3SQCREG4);
    	*batch++ = i915_ggtt_offset(engine->scratch) + 256;
    	*batch++ = 0;
    
    	*batch++ = MI_LOAD_REGISTER_IMM(1);
    	*batch++ = i915_mmio_reg_offset(GEN8_L3SQCREG4);
    	*batch++ = 0x40400000 | GEN8_LQSC_FLUSH_COHERENT_LINES;
    
    	batch = gen8_emit_pipe_control(batch,
    				       PIPE_CONTROL_CS_STALL |
    				       PIPE_CONTROL_DC_FLUSH_ENABLE,
    				       0);
    
    	*batch++ = MI_LOAD_REGISTER_MEM_GEN8 | MI_SRM_LRM_GLOBAL_GTT;
    	*batch++ = i915_mmio_reg_offset(GEN8_L3SQCREG4);
    	*batch++ = i915_ggtt_offset(engine->scratch) + 256;
    	*batch++ = 0;
    
    	return batch;
    }
    
    /*
     * Typically we only have one indirect_ctx and per_ctx batch buffer which are
     * initialized at the beginning and shared across all contexts but this field
     * helps us to have multiple batches at different offsets and select them based
     * on a criteria. At the moment this batch always start at the beginning of the page
     * and at this point we don't have multiple wa_ctx batch buffers.
     *
     * The number of WA applied are not known at the beginning; we use this field
     * to return the no of DWORDS written.
     *
     * It is to be noted that this batch does not contain MI_BATCH_BUFFER_END
     * so it adds NOOPs as padding to make it cacheline aligned.
     * MI_BATCH_BUFFER_END will be added to perctx batch and both of them together
     * makes a complete batch buffer.
     */
    static u32 *gen8_init_indirectctx_bb(struct intel_engine_cs *engine, u32 *batch)
    {
    	/* WaDisableCtxRestoreArbitration:bdw,chv */
    	*batch++ = MI_ARB_ON_OFF | MI_ARB_DISABLE;
    
    	/* WaFlushCoherentL3CacheLinesAtContextSwitch:bdw */
    	if (IS_BROADWELL(engine->i915))
    		batch = gen8_emit_flush_coherentl3_wa(engine, batch);
    
    	/* WaClearSlmSpaceAtContextSwitch:bdw,chv */
    	/* Actual scratch location is at 128 bytes offset */
    	batch = gen8_emit_pipe_control(batch,
    				       PIPE_CONTROL_FLUSH_L3 |
    				       PIPE_CONTROL_GLOBAL_GTT_IVB |
    				       PIPE_CONTROL_CS_STALL |
    				       PIPE_CONTROL_QW_WRITE,
    				       i915_ggtt_offset(engine->scratch) +
    				       2 * CACHELINE_BYTES);
    
    	*batch++ = MI_ARB_ON_OFF | MI_ARB_ENABLE;
    
    	/* Pad to end of cacheline */
    	while ((unsigned long)batch % CACHELINE_BYTES)
    		*batch++ = MI_NOOP;
    
    	/*
    	 * MI_BATCH_BUFFER_END is not required in Indirect ctx BB because
    	 * execution depends on the length specified in terms of cache lines
    	 * in the register CTX_RCS_INDIRECT_CTX
    	 */
    
    	return batch;
    }
    
    static u32 *gen9_init_indirectctx_bb(struct intel_engine_cs *engine, u32 *batch)
    {
    	*batch++ = MI_ARB_ON_OFF | MI_ARB_DISABLE;
    
    	/* WaFlushCoherentL3CacheLinesAtContextSwitch:skl,bxt,glk */
    	batch = gen8_emit_flush_coherentl3_wa(engine, batch);
    
    	/* WaDisableGatherAtSetShaderCommonSlice:skl,bxt,kbl,glk */
    	*batch++ = MI_LOAD_REGISTER_IMM(1);
    	*batch++ = i915_mmio_reg_offset(COMMON_SLICE_CHICKEN2);
    	*batch++ = _MASKED_BIT_DISABLE(
    			GEN9_DISABLE_GATHER_AT_SET_SHADER_COMMON_SLICE);
    	*batch++ = MI_NOOP;
    
    	/* WaClearSlmSpaceAtContextSwitch:kbl */
    	/* Actual scratch location is at 128 bytes offset */
    	if (IS_KBL_REVID(engine->i915, 0, KBL_REVID_A0)) {
    		batch = gen8_emit_pipe_control(batch,
    					       PIPE_CONTROL_FLUSH_L3 |
    					       PIPE_CONTROL_GLOBAL_GTT_IVB |
    					       PIPE_CONTROL_CS_STALL |
    					       PIPE_CONTROL_QW_WRITE,
    					       i915_ggtt_offset(engine->scratch)
    					       + 2 * CACHELINE_BYTES);
    	}
    
    	/* WaMediaPoolStateCmdInWABB:bxt,glk */
    	if (HAS_POOLED_EU(engine->i915)) {
    		/*
    		 * EU pool configuration is setup along with golden context
    		 * during context initialization. This value depends on
    		 * device type (2x6 or 3x6) and needs to be updated based
    		 * on which subslice is disabled especially for 2x6
    		 * devices, however it is safe to load default
    		 * configuration of 3x6 device instead of masking off
    		 * corresponding bits because HW ignores bits of a disabled
    		 * subslice and drops down to appropriate config. Please
    		 * see render_state_setup() in i915_gem_render_state.c for
    		 * possible configurations, to avoid duplication they are
    		 * not shown here again.
    		 */
    		*batch++ = GEN9_MEDIA_POOL_STATE;
    		*batch++ = GEN9_MEDIA_POOL_ENABLE;
    		*batch++ = 0x00777000;
    		*batch++ = 0;
    		*batch++ = 0;
    		*batch++ = 0;
    	}
    
    	*batch++ = MI_ARB_ON_OFF | MI_ARB_ENABLE;
    
    	/* Pad to end of cacheline */
    	while ((unsigned long)batch % CACHELINE_BYTES)
    		*batch++ = MI_NOOP;
    
    	return batch;
    }
    
    static u32 *
    gen10_init_indirectctx_bb(struct intel_engine_cs *engine, u32 *batch)
    {
    	int i;
    
    	/*
    	 * WaPipeControlBefore3DStateSamplePattern: cnl
    	 *
    	 * Ensure the engine is idle prior to programming a
    	 * 3DSTATE_SAMPLE_PATTERN during a context restore.
    	 */
    	batch = gen8_emit_pipe_control(batch,
    				       PIPE_CONTROL_CS_STALL,
    				       0);
    	/*
    	 * WaPipeControlBefore3DStateSamplePattern says we need 4 dwords for
    	 * the PIPE_CONTROL followed by 12 dwords of 0x0, so 16 dwords in
    	 * total. However, a PIPE_CONTROL is 6 dwords long, not 4, which is
    	 * confusing. Since gen8_emit_pipe_control() already advances the
    	 * batch by 6 dwords, we advance the other 10 here, completing a
    	 * cacheline. It's not clear if the workaround requires this padding
    	 * before other commands, or if it's just the regular padding we would
    	 * already have for the workaround bb, so leave it here for now.
    	 */
    	for (i = 0; i < 10; i++)
    		*batch++ = MI_NOOP;
    
    	/* Pad to end of cacheline */
    	while ((unsigned long)batch % CACHELINE_BYTES)
    		*batch++ = MI_NOOP;
    
    	return batch;
    }
    
    #define CTX_WA_BB_OBJ_SIZE (PAGE_SIZE)
    
    static int lrc_setup_wa_ctx(struct intel_engine_cs *engine)
    {
    	struct drm_i915_gem_object *obj;
    	struct i915_vma *vma;
    	int err;
    
    	obj = i915_gem_object_create(engine->i915, CTX_WA_BB_OBJ_SIZE);
    	if (IS_ERR(obj))
    		return PTR_ERR(obj);
    
    	vma = i915_vma_instance(obj, &engine->i915->ggtt.base, NULL);
    	if (IS_ERR(vma)) {
    		err = PTR_ERR(vma);
    		goto err;
    	}
    
    	err = i915_vma_pin(vma, 0, PAGE_SIZE, PIN_GLOBAL | PIN_HIGH);
    	if (err)
    		goto err;
    
    	engine->wa_ctx.vma = vma;
    	return 0;
    
    err:
    	i915_gem_object_put(obj);
    	return err;
    }
    
    static void lrc_destroy_wa_ctx(struct intel_engine_cs *engine)
    {
    	i915_vma_unpin_and_release(&engine->wa_ctx.vma);
    }
    
    typedef u32 *(*wa_bb_func_t)(struct intel_engine_cs *engine, u32 *batch);
    
    static int intel_init_workaround_bb(struct intel_engine_cs *engine)
    {
    	struct i915_ctx_workarounds *wa_ctx = &engine->wa_ctx;
    	struct i915_wa_ctx_bb *wa_bb[2] = { &wa_ctx->indirect_ctx,
    					    &wa_ctx->per_ctx };
    	wa_bb_func_t wa_bb_fn[2];
    	struct page *page;
    	void *batch, *batch_ptr;
    	unsigned int i;
    	int ret;
    
    	if (GEM_WARN_ON(engine->id != RCS))
    		return -EINVAL;
    
    	switch (INTEL_GEN(engine->i915)) {
    	case 10:
    		wa_bb_fn[0] = gen10_init_indirectctx_bb;
    		wa_bb_fn[1] = NULL;
    		break;
    	case 9:
    		wa_bb_fn[0] = gen9_init_indirectctx_bb;
    		wa_bb_fn[1] = NULL;
    		break;
    	case 8:
    		wa_bb_fn[0] = gen8_init_indirectctx_bb;
    		wa_bb_fn[1] = NULL;
    		break;
    	default:
    		MISSING_CASE(INTEL_GEN(engine->i915));
    		return 0;
    	}
    
    	ret = lrc_setup_wa_ctx(engine);
    	if (ret) {
    		DRM_DEBUG_DRIVER("Failed to setup context WA page: %d\n", ret);
    		return ret;
    	}
    
    	page = i915_gem_object_get_dirty_page(wa_ctx->vma->obj, 0);
    	batch = batch_ptr = kmap_atomic(page);
    
    	/*
    	 * Emit the two workaround batch buffers, recording the offset from the
    	 * start of the workaround batch buffer object for each and their
    	 * respective sizes.
    	 */
    	for (i = 0; i < ARRAY_SIZE(wa_bb_fn); i++) {
    		wa_bb[i]->offset = batch_ptr - batch;
    		if (GEM_WARN_ON(!IS_ALIGNED(wa_bb[i]->offset,
    					    CACHELINE_BYTES))) {
    			ret = -EINVAL;
    			break;
    		}
    		if (wa_bb_fn[i])
    			batch_ptr = wa_bb_fn[i](engine, batch_ptr);
    		wa_bb[i]->size = batch_ptr - (batch + wa_bb[i]->offset);
    	}
    
    	BUG_ON(batch_ptr - batch > CTX_WA_BB_OBJ_SIZE);
    
    	kunmap_atomic(batch);
    	if (ret)
    		lrc_destroy_wa_ctx(engine);
    
    	return ret;
    }
    
    static u8 gtiir[] = {
    	[RCS] = 0,
    	[BCS] = 0,
    	[VCS] = 1,
    	[VCS2] = 1,
    	[VECS] = 3,
    };
    
    static void enable_execlists(struct intel_engine_cs *engine)
    {
    	struct drm_i915_private *dev_priv = engine->i915;
    
    	I915_WRITE(RING_HWSTAM(engine->mmio_base), 0xffffffff);
    
    	/*
    	 * Make sure we're not enabling the new 12-deep CSB
    	 * FIFO as that requires a slightly updated handling
    	 * in the ctx switch irq. Since we're currently only
    	 * using only 2 elements of the enhanced execlists the
    	 * deeper FIFO it's not needed and it's not worth adding
    	 * more statements to the irq handler to support it.
    	 */
    	if (INTEL_GEN(dev_priv) >= 11)
    		I915_WRITE(RING_MODE_GEN7(engine),
    			   _MASKED_BIT_DISABLE(GEN11_GFX_DISABLE_LEGACY_MODE));
    	else
    		I915_WRITE(RING_MODE_GEN7(engine),
    			   _MASKED_BIT_ENABLE(GFX_RUN_LIST_ENABLE));
    
    	I915_WRITE(RING_HWS_PGA(engine->mmio_base),
    		   engine->status_page.ggtt_offset);
    	POSTING_READ(RING_HWS_PGA(engine->mmio_base));
    
    	/* Following the reset, we need to reload the CSB read/write pointers */
    	engine->execlists.csb_head = -1;
    }
    
    static int gen8_init_common_ring(struct intel_engine_cs *engine)
    {
    	struct intel_engine_execlists * const execlists = &engine->execlists;
    	int ret;
    
    	ret = intel_mocs_init_engine(engine);
    	if (ret)
    		return ret;
    
    	intel_engine_reset_breadcrumbs(engine);
    	intel_engine_init_hangcheck(engine);
    
    	enable_execlists(engine);
    
    	/* After a GPU reset, we may have requests to replay */
    	if (execlists->first)
    		tasklet_schedule(&execlists->tasklet);
    
    	return 0;
    }
    
    static int gen8_init_render_ring(struct intel_engine_cs *engine)
    {
    	struct drm_i915_private *dev_priv = engine->i915;
    	int ret;
    
    	ret = gen8_init_common_ring(engine);
    	if (ret)
    		return ret;
    
    	/* We need to disable the AsyncFlip performance optimisations in order
    	 * to use MI_WAIT_FOR_EVENT within the CS. It should already be
    	 * programmed to '1' on all products.
    	 *
    	 * WaDisableAsyncFlipPerfMode:snb,ivb,hsw,vlv,bdw,chv
    	 */
    	I915_WRITE(MI_MODE, _MASKED_BIT_ENABLE(ASYNC_FLIP_PERF_DISABLE));
    
    	I915_WRITE(INSTPM, _MASKED_BIT_ENABLE(INSTPM_FORCE_ORDERING));
    
    	return init_workarounds_ring(engine);
    }
    
    static int gen9_init_render_ring(struct intel_engine_cs *engine)
    {
    	int ret;
    
    	ret = gen8_init_common_ring(engine);
    	if (ret)
    		return ret;
    
    	return init_workarounds_ring(engine);
    }
    
    static void reset_irq(struct intel_engine_cs *engine)
    {
    	struct drm_i915_private *dev_priv = engine->i915;
    	int i;
    
    	GEM_BUG_ON(engine->id >= ARRAY_SIZE(gtiir));
    
    	/*
    	 * Clear any pending interrupt state.
    	 *
    	 * We do it twice out of paranoia that some of the IIR are double
    	 * buffered, and if we only reset it once there may still be
    	 * an interrupt pending.
    	 */
    	for (i = 0; i < 2; i++) {
    		I915_WRITE(GEN8_GT_IIR(gtiir[engine->id]),
    			   GT_CONTEXT_SWITCH_INTERRUPT << engine->irq_shift);
    		POSTING_READ(GEN8_GT_IIR(gtiir[engine->id]));
    	}
    	GEM_BUG_ON(I915_READ(GEN8_GT_IIR(gtiir[engine->id])) &
    		   (GT_CONTEXT_SWITCH_INTERRUPT << engine->irq_shift));
    
    	clear_bit(ENGINE_IRQ_EXECLIST, &engine->irq_posted);
    }
    
    static void reset_common_ring(struct intel_engine_cs *engine,
    			      struct i915_request *request)
    {
    	struct intel_engine_execlists * const execlists = &engine->execlists;
    	struct intel_context *ce;
    	unsigned long flags;
    
    	GEM_TRACE("%s seqno=%x\n",
    		  engine->name, request ? request->global_seqno : 0);
    
    	/* See execlists_cancel_requests() for the irq/spinlock split. */
    	local_irq_save(flags);
    
    	reset_irq(engine);
    
    	/*
    	 * Catch up with any missed context-switch interrupts.
    	 *
    	 * Ideally we would just read the remaining CSB entries now that we
    	 * know the gpu is idle. However, the CSB registers are sometimes^W
    	 * often trashed across a GPU reset! Instead we have to rely on
    	 * guessing the missed context-switch events by looking at what
    	 * requests were completed.
    	 */
    	execlists_cancel_port_requests(execlists);
    
    	/* Push back any incomplete requests for replay after the reset. */
    	spin_lock(&engine->timeline->lock);
    	__unwind_incomplete_requests(engine);
    	spin_unlock(&engine->timeline->lock);
    
    	/* Mark all CS interrupts as complete */
    	execlists->active = 0;
    
    	local_irq_restore(flags);
    
    	/*
    	 * If the request was innocent, we leave the request in the ELSP
    	 * and will try to replay it on restarting. The context image may
    	 * have been corrupted by the reset, in which case we may have
    	 * to service a new GPU hang, but more likely we can continue on
    	 * without impact.
    	 *
    	 * If the request was guilty, we presume the context is corrupt
    	 * and have to at least restore the RING register in the context
    	 * image back to the expected values to skip over the guilty request.
    	 */
    	if (!request || request->fence.error != -EIO)
    		return;
    
    	/*
    	 * We want a simple context + ring to execute the breadcrumb update.
    	 * We cannot rely on the context being intact across the GPU hang,
    	 * so clear it and rebuild just what we need for the breadcrumb.
    	 * All pending requests for this context will be zapped, and any
    	 * future request will be after userspace has had the opportunity
    	 * to recreate its own state.
    	 */
    	ce = &request->ctx->engine[engine->id];
    	execlists_init_reg_state(ce->lrc_reg_state,
    				 request->ctx, engine, ce->ring);
    
    	/* Move the RING_HEAD onto the breadcrumb, past the hanging batch */
    	ce->lrc_reg_state[CTX_RING_BUFFER_START+1] =
    		i915_ggtt_offset(ce->ring->vma);
    	ce->lrc_reg_state[CTX_RING_HEAD+1] = request->postfix;
    
    	request->ring->head = request->postfix;
    	intel_ring_update_space(request->ring);
    
    	/* Reset WaIdleLiteRestore:bdw,skl as well */
    	unwind_wa_tail(request);
    }
    
    static int intel_logical_ring_emit_pdps(struct i915_request *rq)
    {
    	struct i915_hw_ppgtt *ppgtt = rq->ctx->ppgtt;
    	struct intel_engine_cs *engine = rq->engine;
    	const int num_lri_cmds = GEN8_3LVL_PDPES * 2;
    	u32 *cs;
    	int i;
    
    	cs = intel_ring_begin(rq, num_lri_cmds * 2 + 2);
    	if (IS_ERR(cs))
    		return PTR_ERR(cs);
    
    	*cs++ = MI_LOAD_REGISTER_IMM(num_lri_cmds);
    	for (i = GEN8_3LVL_PDPES - 1; i >= 0; i--) {
    		const dma_addr_t pd_daddr = i915_page_dir_dma_addr(ppgtt, i);
    
    		*cs++ = i915_mmio_reg_offset(GEN8_RING_PDP_UDW(engine, i));
    		*cs++ = upper_32_bits(pd_daddr);
    		*cs++ = i915_mmio_reg_offset(GEN8_RING_PDP_LDW(engine, i));
    		*cs++ = lower_32_bits(pd_daddr);
    	}
    
    	*cs++ = MI_NOOP;
    	intel_ring_advance(rq, cs);
    
    	return 0;
    }
    
    static int gen8_emit_bb_start(struct i915_request *rq,
    			      u64 offset, u32 len,
    			      const unsigned int flags)
    {
    	u32 *cs;
    	int ret;
    
    	/* Don't rely in hw updating PDPs, specially in lite-restore.
    	 * Ideally, we should set Force PD Restore in ctx descriptor,
    	 * but we can't. Force Restore would be a second option, but
    	 * it is unsafe in case of lite-restore (because the ctx is
    	 * not idle). PML4 is allocated during ppgtt init so this is
    	 * not needed in 48-bit.*/
    	if (rq->ctx->ppgtt &&
    	    (intel_engine_flag(rq->engine) & rq->ctx->ppgtt->pd_dirty_rings) &&
    	    !i915_vm_is_48bit(&rq->ctx->ppgtt->base) &&
    	    !intel_vgpu_active(rq->i915)) {
    		ret = intel_logical_ring_emit_pdps(rq);
    		if (ret)
    			return ret;
    
    		rq->ctx->ppgtt->pd_dirty_rings &= ~intel_engine_flag(rq->engine);
    	}
    
    	cs = intel_ring_begin(rq, 4);
    	if (IS_ERR(cs))
    		return PTR_ERR(cs);
    
    	/*
    	 * WaDisableCtxRestoreArbitration:bdw,chv
    	 *
    	 * We don't need to perform MI_ARB_ENABLE as often as we do (in
    	 * particular all the gen that do not need the w/a at all!), if we
    	 * took care to make sure that on every switch into this context
    	 * (both ordinary and for preemption) that arbitrartion was enabled
    	 * we would be fine. However, there doesn't seem to be a downside to
    	 * being paranoid and making sure it is set before each batch and
    	 * every context-switch.
    	 *
    	 * Note that if we fail to enable arbitration before the request
    	 * is complete, then we do not see the context-switch interrupt and
    	 * the engine hangs (with RING_HEAD == RING_TAIL).
    	 *
    	 * That satisfies both the GPGPU w/a and our heavy-handed paranoia.
    	 */
    	*cs++ = MI_ARB_ON_OFF | MI_ARB_ENABLE;
    
    	/* FIXME(BDW): Address space and security selectors. */
    	*cs++ = MI_BATCH_BUFFER_START_GEN8 |
    		(flags & I915_DISPATCH_SECURE ? 0 : BIT(8)) |
    		(flags & I915_DISPATCH_RS ? MI_BATCH_RESOURCE_STREAMER : 0);
    	*cs++ = lower_32_bits(offset);
    	*cs++ = upper_32_bits(offset);
    	intel_ring_advance(rq, cs);
    
    	return 0;
    }
    
    static void gen8_logical_ring_enable_irq(struct intel_engine_cs *engine)
    {
    	struct drm_i915_private *dev_priv = engine->i915;
    	I915_WRITE_IMR(engine,
    		       ~(engine->irq_enable_mask | engine->irq_keep_mask));
    	POSTING_READ_FW(RING_IMR(engine->mmio_base));
    }
    
    static void gen8_logical_ring_disable_irq(struct intel_engine_cs *engine)
    {
    	struct drm_i915_private *dev_priv = engine->i915;
    	I915_WRITE_IMR(engine, ~engine->irq_keep_mask);
    }
    
    static int gen8_emit_flush(struct i915_request *request, u32 mode)
    {
    	u32 cmd, *cs;
    
    	cs = intel_ring_begin(request, 4);
    	if (IS_ERR(cs))
    		return PTR_ERR(cs);
    
    	cmd = MI_FLUSH_DW + 1;
    
    	/* We always require a command barrier so that subsequent
    	 * commands, such as breadcrumb interrupts, are strictly ordered
    	 * wrt the contents of the write cache being flushed to memory
    	 * (and thus being coherent from the CPU).
    	 */
    	cmd |= MI_FLUSH_DW_STORE_INDEX | MI_FLUSH_DW_OP_STOREDW;
    
    	if (mode & EMIT_INVALIDATE) {
    		cmd |= MI_INVALIDATE_TLB;
    		if (request->engine->id == VCS)
    			cmd |= MI_INVALIDATE_BSD;
    	}
    
    	*cs++ = cmd;
    	*cs++ = I915_GEM_HWS_SCRATCH_ADDR | MI_FLUSH_DW_USE_GTT;
    	*cs++ = 0; /* upper addr */
    	*cs++ = 0; /* value */
    	intel_ring_advance(request, cs);
    
    	return 0;
    }
    
    static int gen8_emit_flush_render(struct i915_request *request,
    				  u32 mode)
    {
    	struct intel_engine_cs *engine = request->engine;
    	u32 scratch_addr =
    		i915_ggtt_offset(engine->scratch) + 2 * CACHELINE_BYTES;
    	bool vf_flush_wa = false, dc_flush_wa = false;
    	u32 *cs, flags = 0;
    	int len;
    
    	flags |= PIPE_CONTROL_CS_STALL;
    
    	if (mode & EMIT_FLUSH) {
    		flags |= PIPE_CONTROL_RENDER_TARGET_CACHE_FLUSH;
    		flags |= PIPE_CONTROL_DEPTH_CACHE_FLUSH;
    		flags |= PIPE_CONTROL_DC_FLUSH_ENABLE;
    		flags |= PIPE_CONTROL_FLUSH_ENABLE;
    	}
    
    	if (mode & EMIT_INVALIDATE) {
    		flags |= PIPE_CONTROL_TLB_INVALIDATE;
    		flags |= PIPE_CONTROL_INSTRUCTION_CACHE_INVALIDATE;
    		flags |= PIPE_CONTROL_TEXTURE_CACHE_INVALIDATE;
    		flags |= PIPE_CONTROL_VF_CACHE_INVALIDATE;
    		flags |= PIPE_CONTROL_CONST_CACHE_INVALIDATE;
    		flags |= PIPE_CONTROL_STATE_CACHE_INVALIDATE;
    		flags |= PIPE_CONTROL_QW_WRITE;
    		flags |= PIPE_CONTROL_GLOBAL_GTT_IVB;
    
    		/*
    		 * On GEN9: before VF_CACHE_INVALIDATE we need to emit a NULL
    		 * pipe control.
    		 */
    		if (IS_GEN9(request->i915))
    			vf_flush_wa = true;
    
    		/* WaForGAMHang:kbl */
    		if (IS_KBL_REVID(request->i915, 0, KBL_REVID_B0))
    			dc_flush_wa = true;
    	}
    
    	len = 6;
    
    	if (vf_flush_wa)
    		len += 6;
    
    	if (dc_flush_wa)
    		len += 12;
    
    	cs = intel_ring_begin(request, len);
    	if (IS_ERR(cs))
    		return PTR_ERR(cs);
    
    	if (vf_flush_wa)
    		cs = gen8_emit_pipe_control(cs, 0, 0);
    
    	if (dc_flush_wa)
    		cs = gen8_emit_pipe_control(cs, PIPE_CONTROL_DC_FLUSH_ENABLE,
    					    0);
    
    	cs = gen8_emit_pipe_control(cs, flags, scratch_addr);
    
    	if (dc_flush_wa)
    		cs = gen8_emit_pipe_control(cs, PIPE_CONTROL_CS_STALL, 0);
    
    	intel_ring_advance(request, cs);
    
    	return 0;
    }
    
    /*
     * Reserve space for 2 NOOPs at the end of each request to be
     * used as a workaround for not being allowed to do lite
     * restore with HEAD==TAIL (WaIdleLiteRestore).
     */
    static void gen8_emit_wa_tail(struct i915_request *request, u32 *cs)
    {
    	/* Ensure there's always at least one preemption point per-request. */
    	*cs++ = MI_ARB_CHECK;
    	*cs++ = MI_NOOP;
    	request->wa_tail = intel_ring_offset(request, cs);
    }
    
    static void gen8_emit_breadcrumb(struct i915_request *request, u32 *cs)
    {
    	/* w/a: bit 5 needs to be zero for MI_FLUSH_DW address. */
    	BUILD_BUG_ON(I915_GEM_HWS_INDEX_ADDR & (1 << 5));
    
    	cs = gen8_emit_ggtt_write(cs, request->global_seqno,
    				  intel_hws_seqno_address(request->engine));
    	*cs++ = MI_USER_INTERRUPT;
    	*cs++ = MI_NOOP;
    	request->tail = intel_ring_offset(request, cs);
    	assert_ring_tail_valid(request->ring, request->tail);
    
    	gen8_emit_wa_tail(request, cs);
    }
    static const int gen8_emit_breadcrumb_sz = 6 + WA_TAIL_DWORDS;
    
    static void gen8_emit_breadcrumb_rcs(struct i915_request *request, u32 *cs)
    {
    	/* We're using qword write, seqno should be aligned to 8 bytes. */
    	BUILD_BUG_ON(I915_GEM_HWS_INDEX & 1);
    
    	cs = gen8_emit_ggtt_write_rcs(cs, request->global_seqno,
    				      intel_hws_seqno_address(request->engine));
    	*cs++ = MI_USER_INTERRUPT;
    	*cs++ = MI_NOOP;
    	request->tail = intel_ring_offset(request, cs);
    	assert_ring_tail_valid(request->ring, request->tail);
    
    	gen8_emit_wa_tail(request, cs);
    }
    static const int gen8_emit_breadcrumb_rcs_sz = 8 + WA_TAIL_DWORDS;
    
    static int gen8_init_rcs_context(struct i915_request *rq)
    {
    	int ret;
    
    	ret = intel_ring_workarounds_emit(rq);
    	if (ret)
    		return ret;
    
    	ret = intel_rcs_context_init_mocs(rq);
    	/*
    	 * Failing to program the MOCS is non-fatal.The system will not
    	 * run at peak performance. So generate an error and carry on.
    	 */
    	if (ret)
    		DRM_ERROR("MOCS failed to program: expect performance issues.\n");
    
    	return i915_gem_render_state_emit(rq);
    }
    
    /**
     * intel_logical_ring_cleanup() - deallocate the Engine Command Streamer
     * @engine: Engine Command Streamer.
     */
    void intel_logical_ring_cleanup(struct intel_engine_cs *engine)
    {
    	struct drm_i915_private *dev_priv;
    
    	/*
    	 * Tasklet cannot be active at this point due intel_mark_active/idle
    	 * so this is just for documentation.
    	 */
    	if (WARN_ON(test_bit(TASKLET_STATE_SCHED,
    			     &engine->execlists.tasklet.state)))
    		tasklet_kill(&engine->execlists.tasklet);
    
    	dev_priv = engine->i915;
    
    	if (engine->buffer) {
    		WARN_ON((I915_READ_MODE(engine) & MODE_IDLE) == 0);
    	}
    
    	if (engine->cleanup)
    		engine->cleanup(engine);
    
    	intel_engine_cleanup_common(engine);
    
    	lrc_destroy_wa_ctx(engine);
    
    	engine->i915 = NULL;
    	dev_priv->engine[engine->id] = NULL;
    	kfree(engine);
    }
    
    static void execlists_set_default_submission(struct intel_engine_cs *engine)
    {
    	engine->submit_request = execlists_submit_request;
    	engine->cancel_requests = execlists_cancel_requests;
    	engine->schedule = execlists_schedule;
    	engine->execlists.tasklet.func = execlists_submission_tasklet;
    
    	engine->park = NULL;
    	engine->unpark = NULL;
    
    	engine->flags |= I915_ENGINE_SUPPORTS_STATS;
    
    	engine->i915->caps.scheduler =
    		I915_SCHEDULER_CAP_ENABLED |
    		I915_SCHEDULER_CAP_PRIORITY;
    	if (engine->i915->preempt_context)
    		engine->i915->caps.scheduler |= I915_SCHEDULER_CAP_PREEMPTION;
    }
    
    static void
    logical_ring_default_vfuncs(struct intel_engine_cs *engine)
    {
    	/* Default vfuncs which can be overriden by each engine. */
    	engine->init_hw = gen8_init_common_ring;
    	engine->reset_hw = reset_common_ring;
    
    	engine->context_pin = execlists_context_pin;
    	engine->context_unpin = execlists_context_unpin;
    
    	engine->request_alloc = execlists_request_alloc;
    
    	engine->emit_flush = gen8_emit_flush;
    	engine->emit_breadcrumb = gen8_emit_breadcrumb;
    	engine->emit_breadcrumb_sz = gen8_emit_breadcrumb_sz;
    
    	engine->set_default_submission = execlists_set_default_submission;
    
    	if (INTEL_GEN(engine->i915) < 11) {
    		engine->irq_enable = gen8_logical_ring_enable_irq;
    		engine->irq_disable = gen8_logical_ring_disable_irq;
    	} else {
    		/*
    		 * TODO: On Gen11 interrupt masks need to be clear
    		 * to allow C6 entry. Keep interrupts enabled at
    		 * and take the hit of generating extra interrupts
    		 * until a more refined solution exists.
    		 */
    	}
    	engine->emit_bb_start = gen8_emit_bb_start;
    }
    
    static inline void
    logical_ring_default_irqs(struct intel_engine_cs *engine)
    {
    	unsigned shift = engine->irq_shift;
    	engine->irq_enable_mask = GT_RENDER_USER_INTERRUPT << shift;
    	engine->irq_keep_mask = GT_CONTEXT_SWITCH_INTERRUPT << shift;
    }
    
    static void
    logical_ring_setup(struct intel_engine_cs *engine)
    {
    	struct drm_i915_private *dev_priv = engine->i915;
    	enum forcewake_domains fw_domains;
    
    	intel_engine_setup_common(engine);
    
    	/* Intentionally left blank. */
    	engine->buffer = NULL;
    
    	fw_domains = intel_uncore_forcewake_for_reg(dev_priv,
    						    RING_ELSP(engine),
    						    FW_REG_WRITE);
    
    	fw_domains |= intel_uncore_forcewake_for_reg(dev_priv,
    						     RING_CONTEXT_STATUS_PTR(engine),
    						     FW_REG_READ | FW_REG_WRITE);
    
    	fw_domains |= intel_uncore_forcewake_for_reg(dev_priv,
    						     RING_CONTEXT_STATUS_BUF_BASE(engine),
    						     FW_REG_READ);
    
    	engine->execlists.fw_domains = fw_domains;
    
    	tasklet_init(&engine->execlists.tasklet,
    		     execlists_submission_tasklet, (unsigned long)engine);
    
    	logical_ring_default_vfuncs(engine);
    	logical_ring_default_irqs(engine);
    }
    
    static int logical_ring_init(struct intel_engine_cs *engine)
    {
    	int ret;
    
    	ret = intel_engine_init_common(engine);
    	if (ret)
    		goto error;
    
    	if (HAS_LOGICAL_RING_ELSQ(engine->i915)) {
    		engine->execlists.submit_reg = engine->i915->regs +
    			i915_mmio_reg_offset(RING_EXECLIST_SQ_CONTENTS(engine));
    		engine->execlists.ctrl_reg = engine->i915->regs +
    			i915_mmio_reg_offset(RING_EXECLIST_CONTROL(engine));
    	} else {
    		engine->execlists.submit_reg = engine->i915->regs +
    			i915_mmio_reg_offset(RING_ELSP(engine));
    	}
    
    	engine->execlists.preempt_complete_status = ~0u;
    	if (engine->i915->preempt_context)
    		engine->execlists.preempt_complete_status =
    			upper_32_bits(engine->i915->preempt_context->engine[engine->id].lrc_desc);
    
    	return 0;
    
    error:
    	intel_logical_ring_cleanup(engine);
    	return ret;
    }
    
    int logical_render_ring_init(struct intel_engine_cs *engine)
    {
    	struct drm_i915_private *dev_priv = engine->i915;
    	int ret;
    
    	logical_ring_setup(engine);
    
    	if (HAS_L3_DPF(dev_priv))
    		engine->irq_keep_mask |= GT_RENDER_L3_PARITY_ERROR_INTERRUPT;
    
    	/* Override some for render ring. */
    	if (INTEL_GEN(dev_priv) >= 9)
    		engine->init_hw = gen9_init_render_ring;
    	else
    		engine->init_hw = gen8_init_render_ring;
    	engine->init_context = gen8_init_rcs_context;
    	engine->emit_flush = gen8_emit_flush_render;
    	engine->emit_breadcrumb = gen8_emit_breadcrumb_rcs;
    	engine->emit_breadcrumb_sz = gen8_emit_breadcrumb_rcs_sz;
    
    	ret = intel_engine_create_scratch(engine, PAGE_SIZE);
    	if (ret)
    		return ret;
    
    	ret = intel_init_workaround_bb(engine);
    	if (ret) {
    		/*
    		 * We continue even if we fail to initialize WA batch
    		 * because we only expect rare glitches but nothing
    		 * critical to prevent us from using GPU
    		 */
    		DRM_ERROR("WA batch buffer initialization failed: %d\n",
    			  ret);
    	}
    
    	return logical_ring_init(engine);
    }
    
    int logical_xcs_ring_init(struct intel_engine_cs *engine)
    {
    	logical_ring_setup(engine);
    
    	return logical_ring_init(engine);
    }
    
    static u32
    make_rpcs(struct drm_i915_private *dev_priv)
    {
    	u32 rpcs = 0;
    
    	/*
    	 * No explicit RPCS request is needed to ensure full
    	 * slice/subslice/EU enablement prior to Gen9.
    	*/
    	if (INTEL_GEN(dev_priv) < 9)
    		return 0;
    
    	/*
    	 * Starting in Gen9, render power gating can leave
    	 * slice/subslice/EU in a partially enabled state. We
    	 * must make an explicit request through RPCS for full
    	 * enablement.
    	*/
    	if (INTEL_INFO(dev_priv)->sseu.has_slice_pg) {
    		rpcs |= GEN8_RPCS_S_CNT_ENABLE;
    		rpcs |= hweight8(INTEL_INFO(dev_priv)->sseu.slice_mask) <<
    			GEN8_RPCS_S_CNT_SHIFT;
    		rpcs |= GEN8_RPCS_ENABLE;
    	}
    
    	if (INTEL_INFO(dev_priv)->sseu.has_subslice_pg) {
    		rpcs |= GEN8_RPCS_SS_CNT_ENABLE;
    		rpcs |= hweight8(INTEL_INFO(dev_priv)->sseu.subslice_mask[0]) <<
    			GEN8_RPCS_SS_CNT_SHIFT;
    		rpcs |= GEN8_RPCS_ENABLE;
    	}
    
    	if (INTEL_INFO(dev_priv)->sseu.has_eu_pg) {
    		rpcs |= INTEL_INFO(dev_priv)->sseu.eu_per_subslice <<
    			GEN8_RPCS_EU_MIN_SHIFT;
    		rpcs |= INTEL_INFO(dev_priv)->sseu.eu_per_subslice <<
    			GEN8_RPCS_EU_MAX_SHIFT;
    		rpcs |= GEN8_RPCS_ENABLE;
    	}
    
    	return rpcs;
    }
    
    static u32 intel_lr_indirect_ctx_offset(struct intel_engine_cs *engine)
    {
    	u32 indirect_ctx_offset;
    
    	switch (INTEL_GEN(engine->i915)) {
    	default:
    		MISSING_CASE(INTEL_GEN(engine->i915));
    		/* fall through */
    	case 11:
    		indirect_ctx_offset =
    			GEN11_CTX_RCS_INDIRECT_CTX_OFFSET_DEFAULT;
    		break;
    	case 10:
    		indirect_ctx_offset =
    			GEN10_CTX_RCS_INDIRECT_CTX_OFFSET_DEFAULT;
    		break;
    	case 9:
    		indirect_ctx_offset =
    			GEN9_CTX_RCS_INDIRECT_CTX_OFFSET_DEFAULT;
    		break;
    	case 8:
    		indirect_ctx_offset =
    			GEN8_CTX_RCS_INDIRECT_CTX_OFFSET_DEFAULT;
    		break;
    	}
    
    	return indirect_ctx_offset;
    }
    
    static void execlists_init_reg_state(u32 *regs,
    				     struct i915_gem_context *ctx,
    				     struct intel_engine_cs *engine,
    				     struct intel_ring *ring)
    {
    	struct drm_i915_private *dev_priv = engine->i915;
    	struct i915_hw_ppgtt *ppgtt = ctx->ppgtt ?: dev_priv->mm.aliasing_ppgtt;
    	u32 base = engine->mmio_base;
    	bool rcs = engine->id == RCS;
    
    	/* A context is actually a big batch buffer with several
    	 * MI_LOAD_REGISTER_IMM commands followed by (reg, value) pairs. The
    	 * values we are setting here are only for the first context restore:
    	 * on a subsequent save, the GPU will recreate this batchbuffer with new
    	 * values (including all the missing MI_LOAD_REGISTER_IMM commands that
    	 * we are not initializing here).
    	 */
    	regs[CTX_LRI_HEADER_0] = MI_LOAD_REGISTER_IMM(rcs ? 14 : 11) |
    				 MI_LRI_FORCE_POSTED;
    
    	CTX_REG(regs, CTX_CONTEXT_CONTROL, RING_CONTEXT_CONTROL(engine),
    		_MASKED_BIT_DISABLE(CTX_CTRL_ENGINE_CTX_RESTORE_INHIBIT |
    				    CTX_CTRL_ENGINE_CTX_SAVE_INHIBIT) |
    		_MASKED_BIT_ENABLE(CTX_CTRL_INHIBIT_SYN_CTX_SWITCH |
    				   (HAS_RESOURCE_STREAMER(dev_priv) ?
    				   CTX_CTRL_RS_CTX_ENABLE : 0)));
    	CTX_REG(regs, CTX_RING_HEAD, RING_HEAD(base), 0);
    	CTX_REG(regs, CTX_RING_TAIL, RING_TAIL(base), 0);
    	CTX_REG(regs, CTX_RING_BUFFER_START, RING_START(base), 0);
    	CTX_REG(regs, CTX_RING_BUFFER_CONTROL, RING_CTL(base),
    		RING_CTL_SIZE(ring->size) | RING_VALID);
    	CTX_REG(regs, CTX_BB_HEAD_U, RING_BBADDR_UDW(base), 0);
    	CTX_REG(regs, CTX_BB_HEAD_L, RING_BBADDR(base), 0);
    	CTX_REG(regs, CTX_BB_STATE, RING_BBSTATE(base), RING_BB_PPGTT);
    	CTX_REG(regs, CTX_SECOND_BB_HEAD_U, RING_SBBADDR_UDW(base), 0);
    	CTX_REG(regs, CTX_SECOND_BB_HEAD_L, RING_SBBADDR(base), 0);
    	CTX_REG(regs, CTX_SECOND_BB_STATE, RING_SBBSTATE(base), 0);
    	if (rcs) {
    		struct i915_ctx_workarounds *wa_ctx = &engine->wa_ctx;
    
    		CTX_REG(regs, CTX_RCS_INDIRECT_CTX, RING_INDIRECT_CTX(base), 0);
    		CTX_REG(regs, CTX_RCS_INDIRECT_CTX_OFFSET,
    			RING_INDIRECT_CTX_OFFSET(base), 0);
    		if (wa_ctx->indirect_ctx.size) {
    			u32 ggtt_offset = i915_ggtt_offset(wa_ctx->vma);
    
    			regs[CTX_RCS_INDIRECT_CTX + 1] =
    				(ggtt_offset + wa_ctx->indirect_ctx.offset) |
    				(wa_ctx->indirect_ctx.size / CACHELINE_BYTES);
    
    			regs[CTX_RCS_INDIRECT_CTX_OFFSET + 1] =
    				intel_lr_indirect_ctx_offset(engine) << 6;
    		}
    
    		CTX_REG(regs, CTX_BB_PER_CTX_PTR, RING_BB_PER_CTX_PTR(base), 0);
    		if (wa_ctx->per_ctx.size) {
    			u32 ggtt_offset = i915_ggtt_offset(wa_ctx->vma);
    
    			regs[CTX_BB_PER_CTX_PTR + 1] =
    				(ggtt_offset + wa_ctx->per_ctx.offset) | 0x01;
    		}
    	}
    
    	regs[CTX_LRI_HEADER_1] = MI_LOAD_REGISTER_IMM(9) | MI_LRI_FORCE_POSTED;
    
    	CTX_REG(regs, CTX_CTX_TIMESTAMP, RING_CTX_TIMESTAMP(base), 0);
    	/* PDP values well be assigned later if needed */
    	CTX_REG(regs, CTX_PDP3_UDW, GEN8_RING_PDP_UDW(engine, 3), 0);
    	CTX_REG(regs, CTX_PDP3_LDW, GEN8_RING_PDP_LDW(engine, 3), 0);
    	CTX_REG(regs, CTX_PDP2_UDW, GEN8_RING_PDP_UDW(engine, 2), 0);
    	CTX_REG(regs, CTX_PDP2_LDW, GEN8_RING_PDP_LDW(engine, 2), 0);
    	CTX_REG(regs, CTX_PDP1_UDW, GEN8_RING_PDP_UDW(engine, 1), 0);
    	CTX_REG(regs, CTX_PDP1_LDW, GEN8_RING_PDP_LDW(engine, 1), 0);
    	CTX_REG(regs, CTX_PDP0_UDW, GEN8_RING_PDP_UDW(engine, 0), 0);
    	CTX_REG(regs, CTX_PDP0_LDW, GEN8_RING_PDP_LDW(engine, 0), 0);
    
    	if (ppgtt && i915_vm_is_48bit(&ppgtt->base)) {
    		/* 64b PPGTT (48bit canonical)
    		 * PDP0_DESCRIPTOR contains the base address to PML4 and
    		 * other PDP Descriptors are ignored.
    		 */
    		ASSIGN_CTX_PML4(ppgtt, regs);
    	}
    
    	if (rcs) {
    		regs[CTX_LRI_HEADER_2] = MI_LOAD_REGISTER_IMM(1);
    		CTX_REG(regs, CTX_R_PWR_CLK_STATE, GEN8_R_PWR_CLK_STATE,
    			make_rpcs(dev_priv));
    
    		i915_oa_init_reg_state(engine, ctx, regs);
    	}
    }
    
    static int
    populate_lr_context(struct i915_gem_context *ctx,
    		    struct drm_i915_gem_object *ctx_obj,
    		    struct intel_engine_cs *engine,
    		    struct intel_ring *ring)
    {
    	void *vaddr;
    	u32 *regs;
    	int ret;
    
    	ret = i915_gem_object_set_to_cpu_domain(ctx_obj, true);
    	if (ret) {
    		DRM_DEBUG_DRIVER("Could not set to CPU domain\n");
    		return ret;
    	}
    
    	vaddr = i915_gem_object_pin_map(ctx_obj, I915_MAP_WB);
    	if (IS_ERR(vaddr)) {
    		ret = PTR_ERR(vaddr);
    		DRM_DEBUG_DRIVER("Could not map object pages! (%d)\n", ret);
    		return ret;
    	}
    	ctx_obj->mm.dirty = true;
    
    	if (engine->default_state) {
    		/*
    		 * We only want to copy over the template context state;
    		 * skipping over the headers reserved for GuC communication,
    		 * leaving those as zero.
    		 */
    		const unsigned long start = LRC_HEADER_PAGES * PAGE_SIZE;
    		void *defaults;
    
    		defaults = i915_gem_object_pin_map(engine->default_state,
    						   I915_MAP_WB);
    		if (IS_ERR(defaults))
    			return PTR_ERR(defaults);
    
    		memcpy(vaddr + start, defaults + start, engine->context_size);
    		i915_gem_object_unpin_map(engine->default_state);
    	}
    
    	/* The second page of the context object contains some fields which must
    	 * be set up prior to the first execution. */
    	regs = vaddr + LRC_STATE_PN * PAGE_SIZE;
    	execlists_init_reg_state(regs, ctx, engine, ring);
    	if (!engine->default_state)
    		regs[CTX_CONTEXT_CONTROL + 1] |=
    			_MASKED_BIT_ENABLE(CTX_CTRL_ENGINE_CTX_RESTORE_INHIBIT);
    	if (ctx == ctx->i915->preempt_context && INTEL_GEN(engine->i915) < 11)
    		regs[CTX_CONTEXT_CONTROL + 1] |=
    			_MASKED_BIT_ENABLE(CTX_CTRL_ENGINE_CTX_RESTORE_INHIBIT |
    					   CTX_CTRL_ENGINE_CTX_SAVE_INHIBIT);
    
    	i915_gem_object_unpin_map(ctx_obj);
    
    	return 0;
    }
    
    static int execlists_context_deferred_alloc(struct i915_gem_context *ctx,
    					    struct intel_engine_cs *engine)
    {
    	struct drm_i915_gem_object *ctx_obj;
    	struct intel_context *ce = &ctx->engine[engine->id];
    	struct i915_vma *vma;
    	uint32_t context_size;
    	struct intel_ring *ring;
    	int ret;
    
    	if (ce->state)
    		return 0;
    
    	context_size = round_up(engine->context_size, I915_GTT_PAGE_SIZE);
    
    	/*
    	 * Before the actual start of the context image, we insert a few pages
    	 * for our own use and for sharing with the GuC.
    	 */
    	context_size += LRC_HEADER_PAGES * PAGE_SIZE;
    
    	ctx_obj = i915_gem_object_create(ctx->i915, context_size);
    	if (IS_ERR(ctx_obj)) {
    		DRM_DEBUG_DRIVER("Alloc LRC backing obj failed.\n");
    		return PTR_ERR(ctx_obj);
    	}
    
    	vma = i915_vma_instance(ctx_obj, &ctx->i915->ggtt.base, NULL);
    	if (IS_ERR(vma)) {
    		ret = PTR_ERR(vma);
    		goto error_deref_obj;
    	}
    
    	ring = intel_engine_create_ring(engine, ctx->ring_size);
    	if (IS_ERR(ring)) {
    		ret = PTR_ERR(ring);
    		goto error_deref_obj;
    	}
    
    	ret = populate_lr_context(ctx, ctx_obj, engine, ring);
    	if (ret) {
    		DRM_DEBUG_DRIVER("Failed to populate LRC: %d\n", ret);
    		goto error_ring_free;
    	}
    
    	ce->ring = ring;
    	ce->state = vma;
    
    	return 0;
    
    error_ring_free:
    	intel_ring_free(ring);
    error_deref_obj:
    	i915_gem_object_put(ctx_obj);
    	return ret;
    }
    
    void intel_lr_context_resume(struct drm_i915_private *dev_priv)
    {
    	struct intel_engine_cs *engine;
    	struct i915_gem_context *ctx;
    	enum intel_engine_id id;
    
    	/* Because we emit WA_TAIL_DWORDS there may be a disparity
    	 * between our bookkeeping in ce->ring->head and ce->ring->tail and
    	 * that stored in context. As we only write new commands from
    	 * ce->ring->tail onwards, everything before that is junk. If the GPU
    	 * starts reading from its RING_HEAD from the context, it may try to
    	 * execute that junk and die.
    	 *
    	 * So to avoid that we reset the context images upon resume. For
    	 * simplicity, we just zero everything out.
    	 */
    	list_for_each_entry(ctx, &dev_priv->contexts.list, link) {
    		for_each_engine(engine, dev_priv, id) {
    			struct intel_context *ce = &ctx->engine[engine->id];
    			u32 *reg;
    
    			if (!ce->state)
    				continue;
    
    			reg = i915_gem_object_pin_map(ce->state->obj,
    						      I915_MAP_WB);
    			if (WARN_ON(IS_ERR(reg)))
    				continue;
    
    			reg += LRC_STATE_PN * PAGE_SIZE / sizeof(*reg);
    			reg[CTX_RING_HEAD+1] = 0;
    			reg[CTX_RING_TAIL+1] = 0;
    
    			ce->state->obj->mm.dirty = true;
    			i915_gem_object_unpin_map(ce->state->obj);
    
    			intel_ring_reset(ce->ring, 0);
    		}
    	}
    }