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 > 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 >
