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Subject[PATCHv3 01/11] videobuf2: add cache management members
Extend vb2_buffer and vb2_queue structs with cache management

V4L2 UAPI already contains two buffer flags which user-space,
supposedly, can use to control buffer cache sync:


None of these, however, do anything at the moment. This patch
set is intended to change it.

Since user-space cache management hints are supposed to be
implemented on a per-buffer basis we need to extend vb2_buffer
struct with two new memebers ->need_cache_sync_on_prepare and
->need_cache_sync_on_finish, which will store corresponding
user-space hints.

In order to preserve the existing behaviour, user-space cache
managements flags will be handled only by those drivers that
permit user-space cache hints. That's the purpose of vb2_queue
->allow_cache_hints member. Driver must set ->allow_cache_hints
during queue initialisation to enable cache management hints

Only drivers that set ->allow_cache_hints during queue initialisation
will handle user-space cache management hints. Otherwise hints
will be ignored.

Signed-off-by: Sergey Senozhatsky <>
include/media/videobuf2-core.h | 10 ++++++++++
1 file changed, 10 insertions(+)

diff --git a/include/media/videobuf2-core.h b/include/media/videobuf2-core.h
index a2b2208b02da..4a19170672ac 100644
--- a/include/media/videobuf2-core.h
+++ b/include/media/videobuf2-core.h
@@ -263,6 +263,10 @@ 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.
* 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
@@ -273,6 +277,8 @@ 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;

struct vb2_plane planes[VB2_MAX_PLANES];
struct list_head queued_entry;
@@ -491,6 +497,9 @@ struct vb2_buf_ops {
* @uses_requests: requests are used for this queue. Set to 1 the first time
* a request is queued. Set to 0 when the queue is canceled.
* If this is 1, then you cannot queue buffers directly.
+ * @allow_cache_hints: when set user-space can pass cache management hints in
+ * order to skip cache flush/invalidation on ->prepare() or/and
+ * ->finish().
* @lock: pointer to a mutex that protects the &struct vb2_queue. The
* driver can set this to a mutex to let the v4l2 core serialize
* the queuing ioctls. If the driver wants to handle locking
@@ -564,6 +573,7 @@ struct vb2_queue {
unsigned requires_requests:1;
unsigned uses_qbuf:1;
unsigned uses_requests:1;
+ unsigned allow_cache_hints:1;

struct mutex *lock;
void *owner;
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