Hi TaoJiang,
On Tue, Jun 18, 2024 at 4:30 PM TaoJiang <tao.jiang_2@xxxxxxx> wrote:
From: Ming Qian <ming.qian@xxxxxxx>
When the memory type is VB2_MEMORY_DMABUF, the v4l2 device can't know
whether the dma buffer is coherent or synchronized.
The videobuf2-core will skip cache syncs as it think the DMA exporter
should take care of cache syncs
But in fact it's likely that the client doesn't
synchronize the dma buf before qbuf() or after dqbuf(). and it's
difficult to find this type of error directly.
I think it's helpful that videobuf2-core can call
dma_buf_end_cpu_access() and dma_buf_begin_cpu_access() to handle the
cache syncs.
Signed-off-by: Ming Qian <ming.qian@xxxxxxx>
Signed-off-by: TaoJiang <tao.jiang_2@xxxxxxx>
---
.../media/common/videobuf2/videobuf2-core.c | 22 +++++++++++++++++++
1 file changed, 22 insertions(+)
Sorry, that patch is incorrect. I believe you're misunderstanding the
way DMA-buf buffers should be managed in the userspace. It's the
userspace responsibility to call the DMA_BUF_IOCTL_SYNC ioctl [1] to
signal start and end of CPU access to the kernel and imply necessary
cache synchronization.
[1] https://docs.kernel.org/driver-api/dma-buf.html#dma-buffer-ioctls
So, really sorry, but it's a NAK.
Best regards,
Tomasz
Hi Tomasz,
Thanks for your explanation, sorry for bothering due to our
misunderstanding
Best regards,
Ming
diff --git a/drivers/media/common/videobuf2/videobuf2-core.c b/drivers/media/common/videobuf2/videobuf2-core.c
index 358f1fe42975..4734ff9cf3ce 100644
--- a/drivers/media/common/videobuf2/videobuf2-core.c
+++ b/drivers/media/common/videobuf2/videobuf2-core.c
@@ -340,6 +340,17 @@ static void __vb2_buf_mem_prepare(struct vb2_buffer *vb)
vb->synced = 1;
for (plane = 0; plane < vb->num_planes; ++plane)
call_void_memop(vb, prepare, vb->planes[plane].mem_priv);
+
+ if (vb->memory != VB2_MEMORY_DMABUF)
+ return;
+ for (plane = 0; plane < vb->num_planes; ++plane) {
+ struct dma_buf *dbuf = vb->planes[plane].dbuf;
+
+ if (!dbuf)
+ continue;
+
+ dma_buf_end_cpu_access(dbuf, vb->vb2_queue->dma_dir);
+ }
}
/*
@@ -356,6 +367,17 @@ static void __vb2_buf_mem_finish(struct vb2_buffer *vb)
vb->synced = 0;
for (plane = 0; plane < vb->num_planes; ++plane)
call_void_memop(vb, finish, vb->planes[plane].mem_priv);
+
+ if (vb->memory != VB2_MEMORY_DMABUF)
+ return;
+ for (plane = 0; plane < vb->num_planes; ++plane) {
+ struct dma_buf *dbuf = vb->planes[plane].dbuf;
+
+ if (!dbuf)
+ continue;
+
+ dma_buf_begin_cpu_access(dbuf, vb->vb2_queue->dma_dir);
+ }
}
/*
--
2.43.0-rc1
