linux-kernel - Re: [PATCHv3 7/8] videobuf2: handle V4L2_MEMORY_FLAG_NON

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Date:   Mon, 26 Jul 2021 13:41:41 +0900
From:   Sergey Senozhatsky <senozhatsky@...omium.org>
To:     Tomasz Figa <tfiga@...omium.org>
Cc:     Sergey Senozhatsky <senozhatsky@...omium.org>,
        Dafna Hirschfeld <dafna.hirschfeld@...labora.com>,
        Hans Verkuil <hverkuil-cisco@...all.nl>,
        Ricardo Ribalda <ribalda@...omium.org>,
        Christoph Hellwig <hch@....de>,
        Mauro Carvalho Chehab <mchehab@...nel.org>,
        linux-media@...r.kernel.org, linux-kernel@...r.kernel.org,
        Collabora Kernel ML <kernel@...labora.com>
Subject: Re: [PATCHv3 7/8] videobuf2: handle V4L2_MEMORY_FLAG_NON_COHERENT
 flag

On (21/07/26 13:22), Tomasz Figa wrote:
> > > I guess ->flags can become u8 for both create-bufs and req-bufs.
> > > We had ->flags in both structs as u32, but then decided to leave
> > > some reserved[] space in req-bufs and switched to u8 there.
> >
> > diff --git a/Documentation/userspace-api/media/v4l/vidioc-create-bufs.rst b/Documentation/userspace-api/media/v4l/vidioc-create-bufs.rst
> > index a048a9f6b7b6..cf633b5a4919 100644
> > --- a/Documentation/userspace-api/media/v4l/vidioc-create-bufs.rst
> > +++ b/Documentation/userspace-api/media/v4l/vidioc-create-bufs.rst
> > @@ -112,13 +112,13 @@ than the number requested.
> >         other changes, then set ``count`` to 0, ``memory`` to
> >         ``V4L2_MEMORY_MMAP`` and ``format.type`` to the buffer type.
> >
> > -    * - __u32
> > +    * - __u8
> >        - ``flags``
> >        - Specifies additional buffer management attributes.
> >         See :ref:`memory-flags`.
> >
> > -    * - __u32
> > -      - ``reserved``\ [6]
> > +    * - __u8
> > +      - ``reserved``\ [27]
> >        - A place holder for future extensions. Drivers and applications
> >         must set the array to zero.
> >
> > diff --git a/drivers/media/common/videobuf2/videobuf2-v4l2.c b/drivers/media/common/videobuf2/videobuf2-v4l2.c
> > index 6edf4508c636..2ae949ec0afa 100644
> > --- a/drivers/media/common/videobuf2/videobuf2-v4l2.c
> > +++ b/drivers/media/common/videobuf2/videobuf2-v4l2.c
> > @@ -694,7 +694,7 @@ static void fill_buf_caps(struct vb2_queue *q, u32 *caps)
> >
> >  static void validate_memory_flags(struct vb2_queue *q,
> >                                   int memory,
> > -                                 u32 *flags)
> > +                                 u8 *flags)
> >  {
> >         if (!q->allow_cache_hints || memory != V4L2_MEMORY_MMAP) {
> >                 /*
> > @@ -711,11 +711,9 @@ static void validate_memory_flags(struct vb2_queue *q,
> >  int vb2_reqbufs(struct vb2_queue *q, struct v4l2_requestbuffers *req)
> >  {
> >         int ret = vb2_verify_memory_type(q, req->memory, req->type);
> > -       u32 flags = req->flags;
> >
> >         fill_buf_caps(q, &req->capabilities);
> > -       validate_memory_flags(q, req->memory, &flags);
> > -       req->flags = flags;
> > +       validate_memory_flags(q, req->memory, &req->flags);
> >         return ret ? ret : vb2_core_reqbufs(q, req->memory,
> >                                             req->flags, &req->count);
> >  }
> > @@ -990,11 +988,9 @@ int vb2_ioctl_reqbufs(struct file *file, void *priv,
> >  {
> >         struct video_device *vdev = video_devdata(file);
> >         int res = vb2_verify_memory_type(vdev->queue, p->memory, p->type);
> > -       u32 flags = p->flags;
> >
> >         fill_buf_caps(vdev->queue, &p->capabilities);
> > -       validate_memory_flags(vdev->queue, p->memory, &flags);
> > -       p->flags = flags;
> > +       validate_memory_flags(vdev->queue, p->memory, &p->flags);
> >         if (res)
> >                 return res;
> >         if (vb2_queue_is_busy(vdev, file))
> > diff --git a/include/uapi/linux/videodev2.h b/include/uapi/linux/videodev2.h
> > index 7973aa0465d2..ad4f7cee53f2 100644
> > --- a/include/uapi/linux/videodev2.h
> > +++ b/include/uapi/linux/videodev2.h
> > @@ -2513,8 +2513,8 @@ struct v4l2_create_buffers {
> >         __u32                   memory;
> >         struct v4l2_format      format;
> >         __u32                   capabilities;
> > -       __u32                   flags;
> > -       __u32                   reserved[6];
> > +       __u8                    flags;
> > +       __u8                    reserved[27];
> >  };
> >
> >  /*
> 
> I don't think we want this UABI churn anymore for a trivial
> simplification in the implementation.

OK, I can scratch it. I thought that for API symmetry we can have
::memory-flags of the same type/size in create-bufs and req-bufs,
but don't have any strong opinion on this.