Re: [PATCH] media: videobuf2-v4l2.c: add vb2_queue_change_type() helper

[Hans Verkuil <hverkuil@xs4all.nl>]

Hi Tomi,

On 12/04/2021 10:12, Tomi Valkeinen wrote:
> On some platforms a video device can capture either video data or
> metadata. The driver can implement vidioc functions for both video and
> metadata, and use a single vb2_queue for the buffers. However, vb2_queue
> requires choosing a single buffer type, which conflicts with the idea of
> capturing either video or metadata.
> 
> The buffer type of vb2_queue can be changed, but it's not obvious how
> this should be done in the drivers. To help this, add a new helper
> function vb2_queue_change_type() which ensures the correct checks and
> documents how it can be used.
> 
> Signed-off-by: Tomi Valkeinen <tomi.valkeinen@ideasonboard.com>
> ---
>  drivers/media/common/videobuf2/videobuf2-v4l2.c | 14 ++++++++++++++
>  include/media/videobuf2-v4l2.h                  | 15 +++++++++++++++
>  2 files changed, 29 insertions(+)
> 
> diff --git a/drivers/media/common/videobuf2/videobuf2-v4l2.c b/drivers/media/common/videobuf2/videobuf2-v4l2.c
> index 7e96f67c60ba..2988bb38ceb1 100644
> --- a/drivers/media/common/videobuf2/videobuf2-v4l2.c
> +++ b/drivers/media/common/videobuf2/videobuf2-v4l2.c
> @@ -939,6 +939,20 @@ void vb2_queue_release(struct vb2_queue *q)
>  }
>  EXPORT_SYMBOL_GPL(vb2_queue_release);
>  
> +int vb2_queue_change_type(struct vb2_queue *q, unsigned int type)
> +{
> +	if (type == q->type)
> +		return 0;
> +
> +	if (vb2_is_busy(q))
> +		return -EBUSY;
> +
> +	q->type = type;
> +
> +	return 0;
> +}
> +EXPORT_SYMBOL_GPL(vb2_queue_change_type);
> +
>  __poll_t vb2_poll(struct vb2_queue *q, struct file *file, poll_table *wait)
>  {
>  	struct video_device *vfd = video_devdata(file);
> diff --git a/include/media/videobuf2-v4l2.h b/include/media/videobuf2-v4l2.h
> index c203047eb834..3e604c1b5e1b 100644
> --- a/include/media/videobuf2-v4l2.h
> +++ b/include/media/videobuf2-v4l2.h
> @@ -261,6 +261,21 @@ int __must_check vb2_queue_init_name(struct vb2_queue *q, const char *name);
>   */
>  void vb2_queue_release(struct vb2_queue *q);
>  
> +/**
> + * vb2_queue_change_type() - change the type of an inactive vb2_queue
> + * @q:		pointer to &struct vb2_queue with videobuf2 queue.
> + *
> + * This function changes the type of the vb2_queue. This is only possible
> + * if the queue is not busy (i.e. no buffers have been queued).

queued -> allocated

> + *
> + * vb2_queue_change_type() can be used to support multiple buffer types using
> + * the same queue. The driver can implement v4l2_ioctl_ops.vidioc_reqbufs and
> + * v4l2_ioctl_ops.vidioc_create_bufs functions and call vb2_queue_change_type()
> + * before calling vb2_ioctl_reqbufs() or vb2_ioctl_create_bufs(), and thus
> + * "lock" the buffer type until the buffers have been released.
> + */
> +int vb2_queue_change_type(struct vb2_queue *q, unsigned int type);
> +
>  /**
>   * vb2_poll() - implements poll userspace operation
>   * @q:		pointer to &struct vb2_queue with videobuf2 queue.
> 

Can you also update vivid to use this function? That would also be a good test.
Check with v4l2-compliance as well. It is not impossible that some changes
have to be made to v4l2-compliance, ping me on irc if that's the case.

Regards,

	Hans