diff --git a/Documentation/DMA-attributes.txt b/Documentation/DMA-attributes.txt index 8f8d97f65d7375a9fc87f4bad9f4a6c8033e8bba..34742fc00ec053f3087c2919de40066773f51970 100644 --- a/Documentation/DMA-attributes.txt +++ b/Documentation/DMA-attributes.txt @@ -156,3 +156,11 @@ accesses to DMA buffers in both privileged "supervisor" and unprivileged subsystem that the buffer is fully accessible at the elevated privilege level (and ideally inaccessible or at least read-only at the lesser-privileged levels). + +DMA_ATTR_OVERWRITE +------------------ + +This is a hint to the DMA-mapping subsystem that the device is expected to +overwrite the entire mapped size, thus the caller does not require any of the +previous buffer contents to be preserved. This allows bounce-buffering +implementations to optimise DMA_FROM_DEVICE transfers. diff --git a/include/linux/dma-mapping.h b/include/linux/dma-mapping.h index 9d39d97e09f4dc82bf6418efb943e816ac5e3493..aa23cade6991fc69930169e7ce062a7483a4d4d4 100644 --- a/include/linux/dma-mapping.h +++ b/include/linux/dma-mapping.h @@ -70,6 +70,14 @@ */ #define DMA_ATTR_PRIVILEGED (1UL << 9) +/* + * This is a hint to the DMA-mapping subsystem that the device is expected + * to overwrite the entire mapped size, thus the caller does not require any + * of the previous buffer contents to be preserved. This allows + * bounce-buffering implementations to optimise DMA_FROM_DEVICE transfers. + */ +#define DMA_ATTR_OVERWRITE (1UL << 10) + /* * A dma_addr_t can hold any valid DMA or bus address for the platform. * It can be given to a device to use as a DMA source or target. A CPU cannot diff --git a/kernel/dma/swiotlb.c b/kernel/dma/swiotlb.c index 2a8c41f12d45064e07d6dc88bd84ca97e234f492..1624d12b60af5d16ac999bfe2a2ae41ddabee811 100644 --- a/kernel/dma/swiotlb.c +++ b/kernel/dma/swiotlb.c @@ -584,7 +584,8 @@ phys_addr_t swiotlb_tbl_map_single(struct device *hwdev, for (i = 0; i < nslots; i++) io_tlb_orig_addr[index+i] = orig_addr + (i << IO_TLB_SHIFT); if (!(attrs & DMA_ATTR_SKIP_CPU_SYNC) && - (dir == DMA_TO_DEVICE || dir == DMA_BIDIRECTIONAL)) + (!(attrs & DMA_ATTR_OVERWRITE) || dir == DMA_TO_DEVICE || + dir == DMA_BIDIRECTIONAL)) swiotlb_bounce(orig_addr, tlb_addr, size, DMA_TO_DEVICE); return tlb_addr;