Re: [PATCH v2 3/3] media: uvcvideo: Remove stream->is_streaming field

[Laurent Pinchart]

On Mon, Jun 02, 2025 at 03:47:50PM +0200, Hans Verkuil wrote:
> On 02/06/2025 15:33, Ricardo Ribalda wrote:
> > On Mon, 2 Jun 2025 at 15:23, Hans Verkuil wrote:
> >> On 02/06/2025 14:59, Ricardo Ribalda wrote:
> >>> The is_streaming field is used by modular PM to know if the device is
> >>> currently streaming or not.
> >>>
> >>> With the transition to vb2 and fop helpers, we can use vb2 functions for
> >>> the same functionality. The great benefit is that vb2 already takes
> >>> track of the streaming state for us.
> >>>
> >>> Signed-off-by: Ricardo Ribalda <ribalda@xxxxxxxxxxxx>
> >>> ---
> >>>  drivers/media/usb/uvc/uvc_queue.c | 11 ++++++++-
> >>>  drivers/media/usb/uvc/uvc_v4l2.c  | 51 ++-------------------------------------
> >>>  drivers/media/usb/uvc/uvcvideo.h  |  1 -
> >>>  3 files changed, 12 insertions(+), 51 deletions(-)
> >>>
> >>> diff --git a/drivers/media/usb/uvc/uvc_queue.c b/drivers/media/usb/uvc/uvc_queue.c
> >>> index 72c5494dee9f46ff61072e7d293bfaddda40e615..dff93bec204428b8aebc09332e0322fa68823fa4 100644
> >>> --- a/drivers/media/usb/uvc/uvc_queue.c
> >>> +++ b/drivers/media/usb/uvc/uvc_queue.c
> >>> @@ -165,12 +165,18 @@ static int uvc_start_streaming(struct vb2_queue *vq, unsigned int count)
> >>>
> >>>       lockdep_assert_irqs_enabled();
> >>>
> >>> +     ret = uvc_pm_get(stream->dev);
> >>> +     if (ret)
> >>> +             return ret;
> >>> +
> >>>       queue->buf_used = 0;
> >>>
> >>>       ret = uvc_video_start_streaming(stream);
> >>
> >> I'm not sure this is correct. See comments below.
> >>
> >>>       if (ret == 0)
> >>>               return 0;
> >>>
> >>> +     uvc_pm_put(stream->dev);
> >>> +
> >>>       spin_lock_irq(&queue->irqlock);
> >>>       uvc_queue_return_buffers(queue, UVC_BUF_STATE_QUEUED);
> >>>       spin_unlock_irq(&queue->irqlock);
> >>> @@ -181,11 +187,14 @@ static int uvc_start_streaming(struct vb2_queue *vq, unsigned int count)
> >>>  static void uvc_stop_streaming(struct vb2_queue *vq)
> >>>  {
> >>>       struct uvc_video_queue *queue = vb2_get_drv_priv(vq);
> >>> +     struct uvc_streaming *stream = uvc_queue_to_stream(queue);
> >>>
> >>>       lockdep_assert_irqs_enabled();
> >>>
> >>> -     if (vq->type != V4L2_BUF_TYPE_META_CAPTURE)
> >>> +     if (vq->type != V4L2_BUF_TYPE_META_CAPTURE) {
> >>> +             uvc_pm_put(stream->dev);
> >>
> >> This doesn't look right, for both video and metadata uvc_pm_get is called,
> >> but only for video is put called.
> > 
> > Please take a look at
> > https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/tree/drivers/media/usb/uvc/uvc_queue.c#n195
> > 
> > start_streaming is not called for metadata nodes, only for video nodes.
> 
> So when you start streaming metadata and no video is streaming, then nothing
> happens. I noticed this before, in fact. Only after you also start to stream
> video will the metadata start to arrive. And it stops again as soon as you
> stop streaming video.
> 
> That's not really how it is supposed to work: whoever starts streaming first
> is the one that calls uvc_video_start_streaming. And only when nobody is streaming
> should uvc_video_stop_streaming be called. That's how it works in other drivers
> (e.g. those that stream both video and vbi, or even more different types of data).
> 
> Fixing this would change the behavior of uvc, and I'm not sure if this is
> something we want. I leave that to Laurent and Hans.

I don't see a use case for capturing metadata only, so I think we can
keep the behaviour as-is.

> If this isn't fixed, then at least add a comment explaining why you test for
> != V4L2_BUF_TYPE_META_CAPTURE before calling uvc_pm_put. It's not obvious.

Agreed.

> >>>               uvc_video_stop_streaming(uvc_queue_to_stream(queue));
> >>
> >> And this is odd too.
> >>
> >>> +     }
> >>
> >> My assumption is that uvc_video_start_streaming and uvc_video_stop_streaming
> >> are valid for both video and meta: i.e. the first time you start streaming
> >> (either video or meta) you call uvc_video_start_streaming. If you were already
> >> streaming for e.g. video, then start streaming metadata (or vice versa), then
> >> you don't need to do anything in start_streaming.
> >>
> >> Same for stop_streaming: only if both video and metadata stopped streaming
> >> is uvc_video_stop_streaming called.
> >>
> >> Please correct me if I am wrong.
> >>
> >> In any case, if I am right, then you have to rework this code accordingly.
> >>
> >> Regardless, you need to test various sequences of streaming video and metadata
> >> in different orders and make sure this is handled correctly.
> > 
> > I have tried streaming and getting frames. After some seconds the
> > device turns off as expected.
> > 
> >>>       spin_lock_irq(&queue->irqlock);
> >>>       uvc_queue_return_buffers(queue, UVC_BUF_STATE_ERROR);
> >>> diff --git a/drivers/media/usb/uvc/uvc_v4l2.c b/drivers/media/usb/uvc/uvc_v4l2.c
> >>> index 7a5ecbefa32c0a6b74c85d7f77a25b433598471e..d4bee0d4334b764c0cf02363b573b55fb44eb228 100644
> >>> --- a/drivers/media/usb/uvc/uvc_v4l2.c
> >>> +++ b/drivers/media/usb/uvc/uvc_v4l2.c
> >>> @@ -617,9 +617,6 @@ static int uvc_v4l2_release(struct file *file)
> >>>
> >>>       uvc_ctrl_cleanup_fh(handle);
> >>>
> >>> -     if (handle->is_streaming)
> >>> -             uvc_pm_put(stream->dev);
> >>> -
> >>>       /* Release the file handle. */
> >>>       vb2_fop_release(file);
> >>>       file->private_data = NULL;
> >>> @@ -677,50 +674,6 @@ static int uvc_ioctl_try_fmt(struct file *file, void *fh,
> >>>       return uvc_v4l2_try_format(stream, fmt, &probe, NULL, NULL);
> >>>  }
> >>>
> >>> -static int uvc_ioctl_streamon(struct file *file, void *fh,
> >>> -                           enum v4l2_buf_type type)
> >>> -{
> >>> -     struct uvc_fh *handle = fh;
> >>> -     struct uvc_streaming *stream = handle->stream;
> >>> -     int ret;
> >>> -
> >>> -     if (handle->is_streaming)
> >>> -             return 0;
> >>> -
> >>> -     ret = uvc_pm_get(stream->dev);
> >>> -     if (ret)
> >>> -             return ret;
> >>> -
> >>> -     ret = vb2_ioctl_streamon(file, fh, type);
> >>> -     if (ret) {
> >>> -             uvc_pm_put(stream->dev);
> >>> -             return ret;
> >>> -     }
> >>> -
> >>> -     handle->is_streaming = true;
> >>> -
> >>> -     return 0;
> >>> -}
> >>> -
> >>> -static int uvc_ioctl_streamoff(struct file *file, void *fh,
> >>> -                            enum v4l2_buf_type type)
> >>> -{
> >>> -     struct uvc_fh *handle = fh;
> >>> -     struct uvc_streaming *stream = handle->stream;
> >>> -     int ret;
> >>> -
> >>> -     ret = vb2_ioctl_streamoff(file, fh, type);
> >>> -     if (ret)
> >>> -             return ret;
> >>> -
> >>> -     if (handle->is_streaming) {
> >>> -             handle->is_streaming = false;
> >>> -             uvc_pm_put(stream->dev);
> >>> -     }
> >>> -
> >>> -     return 0;
> >>> -}
> >>> -
> >>>  static int uvc_ioctl_enum_input(struct file *file, void *fh,
> >>>                               struct v4l2_input *input)
> >>>  {
> >>> @@ -1323,8 +1276,8 @@ const struct v4l2_ioctl_ops uvc_ioctl_ops = {
> >>>       .vidioc_expbuf = vb2_ioctl_expbuf,
> >>>       .vidioc_dqbuf = vb2_ioctl_dqbuf,
> >>>       .vidioc_create_bufs = vb2_ioctl_create_bufs,
> >>> -     .vidioc_streamon = uvc_ioctl_streamon,
> >>> -     .vidioc_streamoff = uvc_ioctl_streamoff,
> >>> +     .vidioc_streamon = vb2_ioctl_streamon,
> >>> +     .vidioc_streamoff = vb2_ioctl_streamoff,
> >>>       .vidioc_enum_input = uvc_ioctl_enum_input,
> >>>       .vidioc_g_input = uvc_ioctl_g_input,
> >>>       .vidioc_s_input = uvc_ioctl_s_input,
> >>> diff --git a/drivers/media/usb/uvc/uvcvideo.h b/drivers/media/usb/uvc/uvcvideo.h
> >>> index 3ddbf065a2cbae40ee48cb06f84ca8f0052990c4..f895f690f7cdc1af942d5f3a5f10e9dd1c956a35 100644
> >>> --- a/drivers/media/usb/uvc/uvcvideo.h
> >>> +++ b/drivers/media/usb/uvc/uvcvideo.h
> >>> @@ -626,7 +626,6 @@ struct uvc_fh {
> >>>       struct uvc_video_chain *chain;
> >>>       struct uvc_streaming *stream;
> >>>       unsigned int pending_async_ctrls;
> >>> -     bool is_streaming;
> >>>  };
> >>>
> >>>  /* ------------------------------------------------------------------------

-- 
Regards,

Laurent Pinchart