Le mardi 28 janvier 2025 à 23:35 +0300, Mikhail Rudenko a écrit :
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..146d7997a0da5989fb081a6f28c e0641fe726e63 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);
Am I correct that this is mostly to prevent the kernel from reading back old data from the cache after an application or other driver did CPU writes ? If so, can't we restrict that to DMA_TO_DEVICE and DMA_BIDIRECTIONAL ?
As for pending kernel writes, they should have been flushed before the buffer is made available for dequeue. And any access while a buffer is queued is concurrent access, which is expected to have undefined behaviour.
- dma_sync_sgtable_for_cpu(buf->dev, sgt, buf->dma_dir);
Isn't there a link to make between buf->dma_dir and direcction before calling this ? Also, shouldn't we use direction insead of buf->dma_dir to possibly limit the scope ?
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);
Similar questions for the end_cpu_access implementation.
Nicolas
return 0; }