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authorJavier Martinez Canillas <javier@osg.samsung.com>2016-07-20 13:18:25 -0300
committerMauro Carvalho Chehab <mchehab@s-opensource.com>2016-08-24 10:09:33 -0300
commit82019205e3a8fc687c4ee6538b57039884be4ccc (patch)
tree16615f54210aa02443d3726e431d393ea2aa401c /drivers/media/v4l2-core
parent14150723659af133e4b205ccf6ff8d93c1384014 (diff)
downloadblackbird-op-linux-82019205e3a8fc687c4ee6538b57039884be4ccc.tar.gz
blackbird-op-linux-82019205e3a8fc687c4ee6538b57039884be4ccc.zip
[media] vb2: remove TODO comment for dma-buf in QBUF
There is a TODO comment about the dma-buf being mapped in VIDIOC_QBUF instead of doing it closer to when the actual DMA is going to happen when the buffers are queued in the driver (i.e: __enqueue_in_driver). But there is a reason to do it earlier in QBUF, and is that userspace has no way to know if a exported dma-buf can be imported successfully and so relies on QBUF succeeding as indication that the dma-buf mapped. If QBUF fails, the application can fallback to another streaming I/O method. But moving the dma-buf mapping later when queueing the buffers can be too late for userspace to recover, since it may had dropped the buffer(s) already when it knows that the dma-buf mapping failed. So remove the TODO instead and change the comment to explain this. Suggested-by: Hans Verkuil <hverkuil@xs4all.nl> Signed-off-by: Javier Martinez Canillas <javier@osg.samsung.com> Signed-off-by: Hans Verkuil <hans.verkuil@cisco.com> Signed-off-by: Mauro Carvalho Chehab <mchehab@s-opensource.com>
Diffstat (limited to 'drivers/media/v4l2-core')
-rw-r--r--drivers/media/v4l2-core/videobuf2-core.c7
1 files changed, 4 insertions, 3 deletions
diff --git a/drivers/media/v4l2-core/videobuf2-core.c b/drivers/media/v4l2-core/videobuf2-core.c
index 3d595186309a..f50ff6f33c6f 100644
--- a/drivers/media/v4l2-core/videobuf2-core.c
+++ b/drivers/media/v4l2-core/videobuf2-core.c
@@ -1273,9 +1273,10 @@ static int __qbuf_dmabuf(struct vb2_buffer *vb, const void *pb)
vb->planes[plane].mem_priv = mem_priv;
}
- /* TODO: This pins the buffer(s) with dma_buf_map_attachment()).. but
- * really we want to do this just before the DMA, not while queueing
- * the buffer(s)..
+ /*
+ * This pins the buffer(s) with dma_buf_map_attachment()). It's done
+ * here instead just before the DMA, while queueing the buffer(s) so
+ * userspace knows sooner rather than later if the dma-buf map fails.
*/
for (plane = 0; plane < vb->num_planes; ++plane) {
ret = call_memop(vb, map_dmabuf, vb->planes[plane].mem_priv);
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