Hi Tomi,
On Mon, Apr 12, 2021 at 02:02:09PM +0300, 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@xxxxxxxxxxxxxxxx>
> ---
> drivers/media/common/videobuf2/videobuf2-v4l2.c | 14 ++++++++++++++
> include/media/videobuf2-v4l2.h | 15 +++++++++++++++
> 2 files changed, 29 insertions(+)
>
Good to see you contributing to the media subsystem. Not sure if you
still remember me from the Common Display Framework discussions. ;)
Anyway, thanks for the patch. I think the code itself is okay, but I'm
wondering why the driver couldn't just have two queues, one for each
type?
Best regards,
Tomasz
> 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..12fa72a664cf 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 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.
> --
> 2.25.1
>
