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authorDaniel Vetter <daniel.vetter@ffwll.ch>2016-03-21 08:24:22 +0100
committerDaniel Vetter <daniel.vetter@ffwll.ch>2016-03-21 09:26:45 +0100
commit87e332d56b2c7dc6733f690c9069f4fe75f21c9d (patch)
treefc83506527f804eb1522e850b121598cefc5e0a1 /Documentation/dma-buf-sharing.txt
parent3c66f4aa7f3cb6579dfe977c05fcb5db25b41cd7 (diff)
downloadlinux-aarch64-87e332d56b2c7dc6733f690c9069f4fe75f21c9d.tar.gz
dma-buf: Update docs for SYNC ioctl
Just a bit of wording polish plus mentioning that it can fail and must be restarted. Requested by Sumit. v2: Fix them typos (Hans). Cc: Chris Wilson <chris@chris-wilson.co.uk> Cc: Tiago Vignatti <tiago.vignatti@intel.com> Cc: Stéphane Marchesin <marcheu@chromium.org> Cc: David Herrmann <dh.herrmann@gmail.com> Cc: Sumit Semwal <sumit.semwal@linaro.org> Cc: Daniel Vetter <daniel.vetter@intel.com> CC: linux-media@vger.kernel.org Cc: dri-devel@lists.freedesktop.org Cc: linaro-mm-sig@lists.linaro.org Cc: intel-gfx@lists.freedesktop.org Cc: devel@driverdev.osuosl.org Cc: Hans Verkuil <hverkuil@xs4all.nl> Acked-by: Sumit Semwal <sumit.semwal@linaro.org> Acked-by: Hans Verkuil <hans.verkuil@cisco.com> Signed-off-by: Daniel Vetter <daniel.vetter@intel.com>
Diffstat (limited to 'Documentation/dma-buf-sharing.txt')
-rw-r--r--Documentation/dma-buf-sharing.txt11
1 files changed, 6 insertions, 5 deletions
diff --git a/Documentation/dma-buf-sharing.txt b/Documentation/dma-buf-sharing.txt
index 32ac32e773e1..ca44c5820585 100644
--- a/Documentation/dma-buf-sharing.txt
+++ b/Documentation/dma-buf-sharing.txt
@@ -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