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Subject[PATCH 1/2] media: vb2: Keep dma-buf buffers mapped until they are freed
Date
From: Pawel Osciak <posciak@chromium.org>

When using vb2 for video decoding, dequeued capture buffers may still
be accessed by the hardware: this is the case when they are used as
reference frames for decoding subsequent frames.

When the buffer is imported with dma-buf, it needs to be mapped before
access. Until now, it was mapped when queuing and unmapped when
dequeuing, which doesn't work for access as a reference frames.

One way to solve this would be to map the buffer again when it is
needed as a reference, but the mapping/unmapping operations can
seriously impact performance. As a result, map the buffer once (when it
is first needed when queued) and keep it mapped until it is freed.

Signed-off-by: Pawel Osciak <posciak@chromium.org>
Reviewed-on: https://chromium-review.googlesource.com/334103
Signed-off-by: Paul Kocialkowski <paul.kocialkowski@bootlin.com>
[Paul: Updated for mainline and changed commit message]
---
drivers/media/common/videobuf2/videobuf2-core.c | 11 +++--------
1 file changed, 3 insertions(+), 8 deletions(-)

diff --git a/drivers/media/common/videobuf2/videobuf2-core.c b/drivers/media/common/videobuf2/videobuf2-core.c
index 70e8c3366f9c..ce9294a635cc 100644
--- a/drivers/media/common/videobuf2/videobuf2-core.c
+++ b/drivers/media/common/videobuf2/videobuf2-core.c
@@ -1196,6 +1196,9 @@ static int __prepare_dmabuf(struct vb2_buffer *vb)
* userspace knows sooner rather than later if the dma-buf map fails.
*/
for (plane = 0; plane < vb->num_planes; ++plane) {
+ if (vb->planes[plane].dbuf_mapped)
+ continue;
+
ret = call_memop(vb, map_dmabuf, vb->planes[plane].mem_priv);
if (ret) {
dprintk(1, "failed to map dmabuf for plane %d\n",
@@ -1758,14 +1761,6 @@ static void __vb2_dqbuf(struct vb2_buffer *vb)

vb->state = VB2_BUF_STATE_DEQUEUED;

- /* unmap DMABUF buffer */
- if (q->memory == VB2_MEMORY_DMABUF)
- for (i = 0; i < vb->num_planes; ++i) {
- if (!vb->planes[i].dbuf_mapped)
- continue;
- call_void_memop(vb, unmap_dmabuf, vb->planes[i].mem_priv);
- vb->planes[i].dbuf_mapped = 0;
- }
call_void_bufop(q, init_buffer, vb);
}

--
2.20.1
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