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    Subject[PATCHv3 02/11] videobuf2: handle V4L2 buffer cache flags
    Date
    Set video buffer cache management flags corresponding to V4L2 cache
    flags.

    Both ->prepare() and ->finish() cache management hints should be
    passed during this stage (buffer preparation), because there is no
    other way for user-space to skip ->finish() cache flush.

    There are two possible alternative approaches:
    - The first one is to move cache sync from ->finish() to dqbuf().
    But this breaks some drivers, that need to fix-up buffers before
    dequeueing them.

    - The second one is to move ->finish() call from ->done() to dqbuf.

    Signed-off-by: Sergey Senozhatsky <senozhatsky@chromium.org>
    ---
    .../media/common/videobuf2/videobuf2-v4l2.c | 49 +++++++++++++++++++
    include/media/videobuf2-core.h | 11 +++++
    2 files changed, 60 insertions(+)

    diff --git a/drivers/media/common/videobuf2/videobuf2-v4l2.c b/drivers/media/common/videobuf2/videobuf2-v4l2.c
    index eb5d5db96552..2a604bd7793a 100644
    --- a/drivers/media/common/videobuf2/videobuf2-v4l2.c
    +++ b/drivers/media/common/videobuf2/videobuf2-v4l2.c
    @@ -199,6 +199,15 @@ static int vb2_fill_vb2_v4l2_buffer(struct vb2_buffer *vb, struct v4l2_buffer *b
    vbuf->request_fd = -1;
    vbuf->is_held = false;

    + /*
    + * Clear buffer cache flags if queue does not support user space hints.
    + * That's to indicate to userspace that these flags won't work.
    + */
    + if (!vb2_queue_allows_cache_hints(q)) {
    + b->flags &= ~V4L2_BUF_FLAG_NO_CACHE_INVALIDATE;
    + b->flags &= ~V4L2_BUF_FLAG_NO_CACHE_CLEAN;
    + }
    +
    if (V4L2_TYPE_IS_MULTIPLANAR(b->type)) {
    switch (b->memory) {
    case VB2_MEMORY_USERPTR:
    @@ -337,6 +346,45 @@ static int vb2_fill_vb2_v4l2_buffer(struct vb2_buffer *vb, struct v4l2_buffer *b
    return 0;
    }

    +static void set_buffer_cache_hints(struct vb2_queue *q,
    + struct vb2_buffer *vb,
    + struct v4l2_buffer *b)
    +{
    + /*
    + * DMA exporter should take care of cache syncs, so we can avoid
    + * explicit ->prepare()/->finish() syncs. For other ->memory types
    + * we always need ->prepare() or/and ->finish() cache sync.
    + */
    + if (q->memory == VB2_MEMORY_DMABUF) {
    + vb->need_cache_sync_on_finish = 0;
    + vb->need_cache_sync_on_prepare = 0;
    + return;
    + }
    +
    + /*
    + * Cache sync/invalidation flags are set by default in order to
    + * preserve existing behaviour for old apps/drivers.
    + */
    + vb->need_cache_sync_on_prepare = 1;
    + vb->need_cache_sync_on_finish = 1;
    +
    + if (!vb2_queue_allows_cache_hints(q))
    + return;
    +
    + /*
    + * ->finish() cache sync can be avoided when queue direction is
    + * TO_DEVICE.
    + */
    + if (q->dma_dir == DMA_TO_DEVICE)
    + vb->need_cache_sync_on_finish = 0;
    +
    + if (b->flags & V4L2_BUF_FLAG_NO_CACHE_INVALIDATE)
    + vb->need_cache_sync_on_finish = 0;
    +
    + if (b->flags & V4L2_BUF_FLAG_NO_CACHE_CLEAN)
    + vb->need_cache_sync_on_prepare = 0;
    +}
    +
    static int vb2_queue_or_prepare_buf(struct vb2_queue *q, struct media_device *mdev,
    struct v4l2_buffer *b, bool is_prepare,
    struct media_request **p_req)
    @@ -381,6 +429,7 @@ static int vb2_queue_or_prepare_buf(struct vb2_queue *q, struct media_device *md
    }

    if (!vb->prepared) {
    + set_buffer_cache_hints(q, vb, b);
    /* Copy relevant information provided by the userspace */
    memset(vbuf->planes, 0,
    sizeof(vbuf->planes[0]) * vb->num_planes);
    diff --git a/include/media/videobuf2-core.h b/include/media/videobuf2-core.h
    index 4a19170672ac..d307869bfb15 100644
    --- a/include/media/videobuf2-core.h
    +++ b/include/media/videobuf2-core.h
    @@ -632,6 +632,17 @@ struct vb2_queue {
    #endif
    };

    +/**
    + * vb2_queue_allows_cache_hints() - Return true if the queue allows cache
    + * and memory consistency hints.
    + *
    + * @q: pointer to &struct vb2_queue with videobuf2 queue
    + */
    +static inline bool vb2_queue_allows_cache_hints(struct vb2_queue *q)
    +{
    + return (q->allow_cache_hints != 0) && (q->memory == VB2_MEMORY_MMAP);
    +}
    +
    /**
    * vb2_plane_vaddr() - Return a kernel virtual address of a given plane.
    * @vb: pointer to &struct vb2_buffer to which the plane in
    --
    2.25.0.265.gbab2e86ba0-goog
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