Re: [PATCH v6 03/14] videobuf2: handle V4L2 buffer cache flags

[Tomasz Figa]

Hi Hans,

On Tue, Jun 2, 2020 at 11:51 AM Hans Verkuil <hverkuil@xxxxxxxxx> wrote:
>
> Hi Sergey,
>
> While doing final testing for this patch series (together with the v4l-utils patch)
> I found one remaining issue:
>
> On 14/05/2020 18:01, Sergey Senozhatsky wrote:
> > From: Sergey Senozhatsky <senozhatsky@xxxxxxxxxxxx>
> >
> > 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 tell V4L2 to avoid ->finish() cache
> > flush.
> >
> > Signed-off-by: Sergey Senozhatsky <senozhatsky@xxxxxxxxxxxx>
> > ---
> >  .../media/common/videobuf2/videobuf2-v4l2.c   | 48 +++++++++++++++++++
> >  include/media/videobuf2-core.h                | 11 +++++
> >  2 files changed, 59 insertions(+)
> >
> > diff --git a/drivers/media/common/videobuf2/videobuf2-v4l2.c b/drivers/media/common/videobuf2/videobuf2-v4l2.c
> > index eb5d5db96552..f13851212cc8 100644
> > --- a/drivers/media/common/videobuf2/videobuf2-v4l2.c
> > +++ b/drivers/media/common/videobuf2/videobuf2-v4l2.c
> > @@ -337,6 +337,53 @@ 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)) {
> > +             /*
> > +              * Clear buffer cache flags if queue does not support user
> > +              * space hints. That's to indicate to userspace that these
> > +              * flags won't work.
> > +              */
> > +             b->flags &= ~V4L2_BUF_FLAG_NO_CACHE_INVALIDATE;
> > +             b->flags &= ~V4L2_BUF_FLAG_NO_CACHE_CLEAN;
> > +             return;
> > +     }
>
> These two flags need to be cleared for VB2_MEMORY_DMABUF as well in the test above.
> This bug is causing v4l2-compliance failures (use the test-media script in contrib/test
> in v4l-utils: 'sudo test-media vim2m').

Would you be able to paste the failures, so that we know that we
reproduce the same problems? Thanks!

Best regards,
Tomasz

>
> It's enough to post a v6.1 for this patch, everything else is fine.
>
> Regards,
>
>         Hans
>
> > +
> > +     /*
> > +      * ->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 +428,7 @@ 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 7f39d9fffc8c..ccc5c498d3e3 100644
> > --- a/include/media/videobuf2-core.h
> > +++ b/include/media/videobuf2-core.h
> > @@ -635,6 +635,17 @@ 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 && 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
> >
>