diff --git a/Documentation/DMA-attributes.txt b/Documentation/DMA-attributes.txt index 6ec8de3fde83..e50b1a4835d2 100644 --- a/Documentation/DMA-attributes.txt +++ b/Documentation/DMA-attributes.txt @@ -148,3 +148,13 @@ 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_PRIVILEGED +------------------- + +Some advanced peripherals such as remote processors and GPUs perform +accesses to DMA buffers in both privileged "supervisor" and unprivileged +"user" modes. This attribute is used to indicate to the DMA-mapping +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). diff --git a/include/linux/dma-mapping.h b/include/linux/dma-mapping.h index 177a3efe4dff..d360c60ee1eb 100644 --- a/include/linux/dma-mapping.h +++ b/include/linux/dma-mapping.h @@ -66,6 +66,14 @@ */ #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 2fcab352906c..23c18f6f69b5 100644 --- a/kernel/dma/swiotlb.c +++ b/kernel/dma/swiotlb.c @@ -593,7 +593,8 @@ found: 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, mapping_size, DMA_TO_DEVICE); return tlb_addr;