[Intel-gfx] [PATCH] dma-buf: Update docs for SYNC ioctl
daniel.vetter at ffwll.ch
Mon Mar 21 07:51:45 UTC 2016
Just a bit of wording polish plus mentioning that it can fail and must
Requested by Sumit.
v2: Fix them typos (Hans).
Cc: Chris Wilson <chris at chris-wilson.co.uk>
Cc: Tiago Vignatti <tiago.vignatti at intel.com>
Cc: Stéphane Marchesin <marcheu at chromium.org>
Cc: David Herrmann <dh.herrmann at gmail.com>
Cc: Sumit Semwal <sumit.semwal at linaro.org>
Cc: Daniel Vetter <daniel.vetter at intel.com>
CC: linux-media at vger.kernel.org
Cc: dri-devel at lists.freedesktop.org
Cc: linaro-mm-sig at lists.linaro.org
Cc: intel-gfx at lists.freedesktop.org
Cc: devel at driverdev.osuosl.org
Cc: Hans Verkuil <hverkuil at xs4all.nl>
Acked-by: Sumit Semwal <sumit.semwal at linaro.org>
Signed-off-by: Daniel Vetter <daniel.vetter at intel.com>
Documentation/dma-buf-sharing.txt | 11 ++++++-----
drivers/dma-buf/dma-buf.c | 2 +-
2 files changed, 7 insertions(+), 6 deletions(-)
diff --git a/Documentation/dma-buf-sharing.txt b/Documentation/dma-buf-sharing.txt
index 32ac32e773e1..ca44c5820585 100644
@@ -352,7 +352,8 @@ Being able to mmap an export dma-buf buffer object has 2 main use-cases:
No special interfaces, userspace simply calls mmap on the dma-buf fd, making
sure that the cache synchronization ioctl (DMA_BUF_IOCTL_SYNC) is *always*
- used when the access happens. This is discussed next paragraphs.
+ used when the access happens. Note that DMA_BUF_IOCTL_SYNC can fail with
+ -EAGAIN or -EINTR, in which case it must be restarted.
Some systems might need some sort of cache coherency management e.g. when
CPU and GPU domains are being accessed through dma-buf at the same time. To
@@ -366,10 +367,10 @@ Being able to mmap an export dma-buf buffer object has 2 main use-cases:
want (with the new data being consumed by the GPU or say scanout device)
- munmap once you don't need the buffer any more
- Therefore, for correctness and optimal performance, systems with the memory
- cache shared by the GPU and CPU i.e. the "coherent" and also the
- "incoherent" are always required to use SYNC_START and SYNC_END before and
- after, respectively, when accessing the mapped address.
+ For correctness and optimal performance, it is always required to use
+ SYNC_START and SYNC_END before and after, respectively, when accessing the
+ mapped address. Userspace cannot rely on coherent access, even when there
+ are systems where it just works without calling these ioctls.
2. Supporting existing mmap interfaces in importers
diff --git a/drivers/dma-buf/dma-buf.c b/drivers/dma-buf/dma-buf.c
index 774a60f4309a..4a2c07ee6677 100644
@@ -612,7 +612,7 @@ EXPORT_SYMBOL_GPL(dma_buf_begin_cpu_access);
* @dmabuf: [in] buffer to complete cpu access for.
* @direction: [in] length of range for cpu access.
- * This call must always succeed.
+ * Can return negative error values, returns 0 on success.
int dma_buf_end_cpu_access(struct dma_buf *dmabuf,
enum dma_data_direction direction)
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