diff options
author | Jason Ekstrand <jason@jlekstrand.net> | 2021-06-17 22:42:58 +0300 |
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committer | Daniel Vetter <daniel.vetter@ffwll.ch> | 2021-06-17 22:46:37 +0300 |
commit | 51f52547df700819db0d0e2b17b677cb209212b4 (patch) | |
tree | ddef6a516dbfc701c9f9835cf696a5ec2b3f6f15 /include/uapi | |
parent | d35c97f606a1398b58e14e7cb8a7c67f7817be2a (diff) | |
download | linux-51f52547df700819db0d0e2b17b677cb209212b4.tar.xz |
dma-buf: Document DMA_BUF_IOCTL_SYNC (v3)
This adds a new "DMA Buffer ioctls" section to the dma-buf docs and adds
documentation for DMA_BUF_IOCTL_SYNC.
v2 (Daniel Vetter):
- Fix a couple typos
- Add commentary about synchronization with other devices
- Use item list format for describing flags
v3 (Pekka Paalanen):
- Clarify stalling requirements.
- Be more clear that that DMA_BUF_IOCTL_SYNC with SINC_END has to be
called before more GPU work happens.
Signed-off-by: Jason Ekstrand <jason@jlekstrand.net>
Reviewed-by: Daniel Vetter <daniel.vetter@ffwll.ch>
Acked-by: Christian König <christian.koenig@amd.com>
Acked-by: Pekka Paalanen <pekka.paalanen@collabora.com>
Cc: Sumit Semwal <sumit.semwal@linaro.org>
Signed-off-by: Daniel Vetter <daniel.vetter@ffwll.ch>
Link: https://patchwork.freedesktop.org/patch/msgid/20210617194258.579011-1-jason@jlekstrand.net
Diffstat (limited to 'include/uapi')
-rw-r--r-- | include/uapi/linux/dma-buf.h | 50 |
1 files changed, 49 insertions, 1 deletions
diff --git a/include/uapi/linux/dma-buf.h b/include/uapi/linux/dma-buf.h index 7f30393b92c3..8e4a2ca0bcbf 100644 --- a/include/uapi/linux/dma-buf.h +++ b/include/uapi/linux/dma-buf.h @@ -22,8 +22,56 @@ #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 must 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. + * + * The synchronization provided via DMA_BUF_IOCTL_SYNC only provides cache + * coherency. It does not prevent other processes or devices from + * accessing the memory at the same time. If synchronization with a GPU or + * other device driver is required, it is the client's responsibility to + * wait for buffer to be ready for reading or writing before calling this + * ioctl with DMA_BUF_SYNC_START. Likewise, the client must ensure that + * follow-up work is not submitted to GPU or other device driver until + * after this ioctl has been called with DMA_BUF_SYNC_END? + * + * If the driver or API with which the client is interacting uses implicit + * synchronization, waiting for prior work to complete can be done via + * poll() on the DMA buffer file descriptor. If the driver or API requires + * explicit synchronization, the client may have to wait on a sync_file or + * other synchronization primitive outside the scope of the DMA buffer API. + */ 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_WRITE: + * 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; }; |