Re: [PATCH v1 3/5] media: stm32-dcmipp: STM32 DCMIPP camera interface driver

Laurent Pinchart
2023-08-24T13:05:05Z

On Thu, Aug 24, 2023 at 12:26:42PM +0000, Sakari Ailus wrote:
> On Thu, Aug 24, 2023 at 01:09:34PM +0200, Alain Volmat wrote:
> > Hi Sakari,
> >
> > thanks a lot for the review. I've already taken care of the comments I got
> > from Dan and will also add fixes for your comments as well before
> > pushing the v2. Before going into that I thought I'd better clarify the
> > framerate part which seems the most tricky part.
> >
> > On Mon, Aug 07, 2023 at 09:29:55AM +0000, Sakari Ailus wrote:
>
> ...
>
> > > > +static int dcmipp_byteproc_g_frame_interval(struct v4l2_subdev *sd,
> > > > + struct v4l2_subdev_frame_interval *fi)
> > > > +{
> > > > + struct dcmipp_byteproc_device *byteproc = v4l2_get_subdevdata(sd);
> > > > +
> > > > + if (IS_SINK(fi->pad))
> > > > + fi->interval = byteproc->sink_interval;
> > > > + else
> > > > + fi->interval = byteproc->src_interval;
> > > > +
> > > > + return 0;
> > > > +}
> > > > +
> > > > +static int dcmipp_byteproc_s_frame_interval(struct v4l2_subdev *sd,
> > > > + struct v4l2_subdev_frame_interval *fi)
> > > > +{
> > > > + struct dcmipp_byteproc_device *byteproc = v4l2_get_subdevdata(sd);
> > > > +
> > > > + mutex_lock(&byteproc->lock);
> > > > +
> > > > + if (byteproc->streaming) {
> > > > + mutex_unlock(&byteproc->lock);
> > > > + return -EBUSY;
> > > > + }
> > > > +
> > > > + if (fi->interval.numerator == 0 || fi->interval.denominator == 0)
> > > > + fi->interval = byteproc->sink_interval;
> > > > +
> > > > + if (IS_SINK(fi->pad)) {
> > > > + /*
> > > > + * Setting sink frame interval resets frame skipping.
> > > > + * Sink frame interval is propagated to src.
> > > > + */
> > > > + byteproc->frate = 0;
> > > > + byteproc->sink_interval = fi->interval;
> > > > + byteproc->src_interval = byteproc->sink_interval;
> > >
> > > Is this used for anything else than configure skipping?
> > >
> > > I think I'd just have a control for it in that case.
> > >
> > > I don't think exposing frame interval configuration is necessarily even
> > > meaningful for a device that just processes data but does not produce it.
> >
> > The DCMIPP is able to perform frame drop, 1/2, 1/4, 1/8 basically.
> > As Dan pointed me out, indeed setting frame interval as we did on both
> > sink and source pad isn't a defined behavior. I first thought that
> > using the frame interval was the proper way to do that but that is
> > indeed only used on producers such as sensors ....
> > Which ctrl would you propose in such case ?
>
> We don't have one, AFAIK, and I think it may be unlikely this will be
> needed elsewhere. So I'd use a private control.
>
> I wonder what others think. Cc Laurent as well.

What are the use cases for this feature ?

--
Regards,

Laurent Pinchart