On Tue, Jan 28, 2025 at 9:36 PM Mikhail Rudenko mike.rudenko@gmail.com wrote:
When support for V4L2_FLAG_MEMORY_NON_CONSISTENT was removed in commit 129134e5415d ("media: media/v4l2: remove V4L2_FLAG_MEMORY_NON_CONSISTENT flag"), vb2_dc_dmabuf_ops_{begin,end}_cpu_access() functions were made no-ops. Later, when support for V4L2_MEMORY_FLAG_NON_COHERENT was introduced in commit c0acf9cfeee0 ("media: videobuf2: handle V4L2_MEMORY_FLAG_NON_COHERENT flag"), the above functions remained no-ops, making cache maintenance for non-coherent dmabufs allocated by dma-contig impossible.
Fix this by reintroducing dma_sync_sgtable_for_{cpu,device} and {flush,invalidate}_kernel_vmap_range calls to vb2_dc_dmabuf_ops_{begin,end}_cpu_access() functions for non-coherent buffers.
Fixes: c0acf9cfeee0 ("media: videobuf2: handle V4L2_MEMORY_FLAG_NON_COHERENT flag") Cc: stable@vger.kernel.org Signed-off-by: Mikhail Rudenko mike.rudenko@gmail.com
.../media/common/videobuf2/videobuf2-dma-contig.c | 22 ++++++++++++++++++++++ 1 file changed, 22 insertions(+)
diff --git a/drivers/media/common/videobuf2/videobuf2-dma-contig.c b/drivers/media/common/videobuf2/videobuf2-dma-contig.c index bb0b7fa67b539aa73ad5ccf3c3bc318e26f8a4cb..146d7997a0da5989fb081a6f28ce0641fe726e63 100644 --- a/drivers/media/common/videobuf2/videobuf2-dma-contig.c +++ b/drivers/media/common/videobuf2/videobuf2-dma-contig.c @@ -427,6 +427,17 @@ static int vb2_dc_dmabuf_ops_begin_cpu_access(struct dma_buf *dbuf, enum dma_data_direction direction) {
struct vb2_dc_buf *buf = dbuf->priv;struct sg_table *sgt = buf->dma_sgt;if (!buf->non_coherent_mem)return 0;if (buf->vaddr)invalidate_kernel_vmap_range(buf->vaddr, buf->size);dma_sync_sgtable_for_cpu(buf->dev, sgt, buf->dma_dir);return 0;}
@@ -434,6 +445,17 @@ static int vb2_dc_dmabuf_ops_end_cpu_access(struct dma_buf *dbuf, enum dma_data_direction direction) {
struct vb2_dc_buf *buf = dbuf->priv;struct sg_table *sgt = buf->dma_sgt;if (!buf->non_coherent_mem)return 0;if (buf->vaddr)flush_kernel_vmap_range(buf->vaddr, buf->size);dma_sync_sgtable_for_device(buf->dev, sgt, buf->dma_dir);return 0;}
I took some time (over)thinking the kernel vmap range synchronization, because these functions can be called both from the kernel space using respective dma_buf_*() kAPI and also from the user space using the DMA_BUF_SYNC IOCTLs, so we could in theory have the multiple invocations racing with each other, but then I realized that we don't really provide any guarantees for concurrent writes and reads from the CPU, so I believe this should work fine. Sorry for the delay.
Acked-by: Tomasz Figa tfiga@chromium.org
Let me add @Christoph Hellwig and @Robin Murphy just in case I'm wrong on that, though... Hans, let's give them some time to take a look before applying this.
Best regards, Tomasz