Re: [PATCHv3 7/8] videobuf2: handle V4L2_MEMORY_FLAG_NON_COHERENT flag

Tomasz Figa
2021-07-26T04:22:29Z

On Mon, Jul 26, 2021 at 1:20 PM Sergey Senozhatsky
<senozhatsky@chromium.org> wrote:
>
> On (21/07/26 13:05), Sergey Senozhatsky wrote:
> > On (21/07/26 10:40), Sergey Senozhatsky wrote:
> > > On (21/07/22 19:33), Dafna Hirschfeld wrote:
> > > [..]
> > > > > 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);
> > > > > - return ret ? ret : vb2_core_reqbufs(q, req->memory, 0, &req->count);
> > > > > + validate_memory_flags(q, req->memory, &flags);
> > > > > + req->flags = flags;
> > > >
> > > > you can do instead
> > > >
> > > > validate_memory_flags(q, req->memory, &req->flags);
> > >
> > > ->flags are u32 for create-bufs and u8 for reqi-bufs. So `*flags = <value>`
> > > can write to ->reserved[] for req-bufs (if the value is huge enough).
> >
> > 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.
>
> Something like this
>
> ---
>
> 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.

Best regards,
Tomasz