This adds a new "DMA Buffer ioctls" section to the dma-buf docs and adds documentation for DMA_BUF_IOCTL_SYNC.
Signed-off-by: Jason Ekstrand jason@jlekstrand.net Cc: Daniel Vetter daniel.vetter@ffwll.ch Cc: Christian König christian.koenig@amd.com Cc: Sumit Semwal sumit.semwal@linaro.org --- Documentation/driver-api/dma-buf.rst | 8 +++++++ include/uapi/linux/dma-buf.h | 32 +++++++++++++++++++++++++++- 2 files changed, 39 insertions(+), 1 deletion(-)
diff --git a/Documentation/driver-api/dma-buf.rst b/Documentation/driver-api/dma-buf.rst index 7f37ec30d9fd7..784f84fe50a5e 100644 --- a/Documentation/driver-api/dma-buf.rst +++ b/Documentation/driver-api/dma-buf.rst @@ -88,6 +88,9 @@ consider though: - The DMA buffer FD is also pollable, see `Implicit Fence Poll Support`_ below for details.
+- The DMA buffer FD also supports a few dma-buf-specific ioctls, see + `DMA Buffer ioctls`_ below for details. + Basic Operation and Device DMA Access ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
@@ -106,6 +109,11 @@ Implicit Fence Poll Support .. kernel-doc:: drivers/dma-buf/dma-buf.c :doc: implicit fence polling
+DMA Buffer ioctls +~~~~~~~~~~~~~~~~~ + +.. kernel-doc:: include/uapi/linux/dma-buf.h + Kernel Functions and Structures Reference ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
diff --git a/include/uapi/linux/dma-buf.h b/include/uapi/linux/dma-buf.h index 7f30393b92c3b..1f67ced853b14 100644 --- a/include/uapi/linux/dma-buf.h +++ b/include/uapi/linux/dma-buf.h @@ -22,8 +22,38 @@
#include <linux/types.h>
-/* begin/end dma-buf functions used for userspace mmap. */ +/** + * struct dma_buf_sync - Synchronize with CPU access. + * + * When a DMA buffer is accessed from the CPU via mmap, it is not always + * possible to guarantee coherency between the CPU-visible map and underlying + * memory. To manage coherency, DMA_BUF_IOCTL_SYNC must be used to bracket + * any CPU access to give the kernel the chance to shuffle memory around if + * needed. + * + * Prior to accessing the map, the client should call DMA_BUF_IOCTL_SYNC + * with DMA_BUF_SYNC_START and the appropriate read/write flags. Once the + * access is complete, the client should call DMA_BUF_IOCTL_SYNC with + * DMA_BUF_SYNC_END and the same read/write flags. + */ struct dma_buf_sync { + /** + * @flags: Set of access flags + * + * - DMA_BUF_SYNC_START: Indicates the start of a map access + * session. + * + * - DMA_BUF_SYNC_END: Indicates the end of a map access session. + * + * - DMA_BUF_SYNC_READ: Indicates that the mapped DMA buffer will + * be read by the client via the CPU map. + * + * - DMA_BUF_SYNC_READ: Indicates that the mapped DMA buffer will + * be written by the client via the CPU map. + * + * - DMA_BUF_SYNC_RW: An alias for DMA_BUF_SYNC_READ | + * DMA_BUF_SYNC_WRITE. + */ __u64 flags; };