On (20/11/30 11:02), Hans Verkuil wrote:
> > @@ -414,6 +414,20 @@ static int __vb2_queue_alloc(struct vb2_queue *q, enum vb2_memory memory,
> > vb->index = q->num_buffers + buffer;
> > vb->type = q->type;
> > vb->memory = memory;
> > + /*
> > + * A workaround fix. We need to set these flags here so that
> > + * videobuf2 core will call ->prepare()/->finish() cache
> > + * sync/flush on vb2 buffers when appropriate. Otherwise, for
> > + * backends that don't rely on V4L2 (perhaps dvb) these flags
> > + * will always be false and, hence, videobuf2 core will skip
> > + * cache sync/flush operations. However, we can avoid explicit
> > + * ->prepare() and ->finish() cache sync for DMABUF buffers,
> > + * because DMA exporter takes care of it.
> > + */
> > + if (q->memory != VB2_MEMORY_DMABUF) {
> > + vb->need_cache_sync_on_prepare = 1;
> > + vb->need_cache_sync_on_finish = 1;
> > + }
>
> Is this a work-around fix? Isn't this just a bug fix? It seems reasonable
> to always set this when allocating buffers for a queue. And for v4l2 these
> values can be changed if supported by the driver (allow_cache_hints is set).
Yes, it's a bug fix. It's a workaround bug fix in a sense that a proper
bug fix is to rename these flags and invert them (and patch all the
functions that set and test them). A sneak preview of what's in my tree:
---
diff --git a/include/media/videobuf2-core.h b/include/media/videobuf2-core.h
index bd78f6c7f342..3b79042d9d5c 100644
--- a/include/media/videobuf2-core.h
+++ b/include/media/videobuf2-core.h
@@ -264,10 +264,10 @@ struct vb2_buffer {
* after the 'buf_finish' op is called.
* copied_timestamp: the timestamp of this capture buffer was copied
* from an output buffer.
- * need_cache_sync_on_prepare: when set buffer's ->prepare() function
- * performs cache sync/invalidation.
- * need_cache_sync_on_finish: when set buffer's ->finish() function
- * performs cache sync/invalidation.
+ * no_cache_sync_on_prepare: when set buffer's ->prepare() function
+ * skips cache sync/invalidation.
+ * no_cache_sync_on_finish: when set buffer's ->finish() function
+ * skips cache sync/invalidation.
* queued_entry: entry on the queued buffers list, which holds
* all buffers queued from userspace
* done_entry: entry on the list that stores all buffers ready
@@ -278,8 +278,8 @@ struct vb2_buffer {
unsigned int synced:1;
unsigned int prepared:1;
unsigned int copied_timestamp:1;
- unsigned int need_cache_sync_on_prepare:1;
- unsigned int need_cache_sync_on_finish:1;
+ unsigned int no_cache_sync_on_prepare:1;
+ unsigned int no_cache_sync_on_finish:1;
struct vb2_plane planes[VB2_MAX_PLANES];
struct list_head queued_entry;
---
and it's much bigger than a 3-liner ("workaround") fix.
> So the comment would be:
>
> /*
> * We need to set these flags here so that the videobuf2 core
> * will call ->prepare()/->finish() cache sync/flush on vb2
> * buffers when appropriate. However, we can avoid explicit
> * ->prepare() and ->finish() cache sync for DMABUF buffers,
> * because DMA exporter takes care of it.
> */
>
> The commit message would need to be modified as well.
OK.
-ss
