Re: [PATCH] media: v4l2-subdev: Support enable/disable_streams for single-pad subdevs

[Tomi Valkeinen]

On 25/03/2024 19:52, Sakari Ailus wrote:
> Moi,
>
> On Mon, Mar 25, 2024 at 03:43:01PM +0200, Tomi Valkeinen wrote:
> > On 25/03/2024 15:02, Sakari Ailus wrote:
> > > Moi,
> > >
> > > Thanks for the patch.
> > >
> > > On Mon, Mar 25, 2024 at 02:50:55PM +0200, Laurent Pinchart wrote:
> > > > Hi Tomi,
> > > >
> > > > On Mon, Mar 25, 2024 at 02:43:23PM +0200, Tomi Valkeinen wrote:
> > > > > Currently a subdevice with a single pad, e.g. a sensor subdevice, must
> > > > > use the v4l2_subdev_video_ops.s_stream op, instead of
> > > > > v4l2_subdev_pad_ops.enable/disable_streams. This is because the
> > > > > enable/disable_streams machinery requires a routing table which a subdev
> > > > > cannot have with a single pad.
> > > > >
> > > > > Implement enable/disable_streams support for these single-pad subdevices
> > > > > by assuming an implicit stream 0 when the subdevice has only one pad.
> > > > >
> > > > > Signed-off-by: Tomi Valkeinen <tomi.valkeinen@xxxxxxxxxxxxxxxx>
> > > > > ---
> > > > > Even though I did send this patch, I'm not sure if this is necessary.
> > > > > s_stream works fine for the subdevs with a single pad. With the upcoming
> > > > > internal pads, adding an internal pad to the subdev will create a
> > > > > routing table, and enable/disable_streams would get "fixed" that way.
> > >
> > > I'd like to get rid of a redundant way to control streaming.
> >
> > We can't get rid of it anyway, can we? We're not going to convert old
> > drivers to streams.
>
> I'd expect to do that but it'd take a long time. That being said, I think
> we need to consider devices without pads (VCMs) so it may well be this
> would remain after all.
>
> > For new drivers, yes, we shouldn't use s_stream. But is the answer for new
> > sensor drivers this patch, or requiring an internal pad?
>
> For new drivers I'd like to see an internal pad in fact.
> {enable,disable}_streams is still internal to the kernel.

So, you think this patch should be dropped?

> > > > > So perhaps the question is, do we want to support single-pad subdevs in
> > > > > the future, in which case something like this patch is necessary, or
> > > > > will all modern source subdev drivers have internal pads, in which
> > > > > case this is not needed...
> > > >
> > > > I think the latter would be best. I however can't guarantee we won't
> > > > have valid use cases for (enable|disable)_streams on single-pad subdevs
> > > > though, so you patch could still be interesting.
> > >
> > > Instead of the number of pads, could we use instead the
> > > V4L2_SUBDEV_FL_STREAMS flag or whether g_routing op is supported to
> > > determine the need for this?
> >
> > Maybe, but are they better? Do you see some issue with checking for the
> > number of pads? I considered a few options, but then thought that the most
> > safest test for this case is 1) one pad 2) enable/disable_streams
> > implemented.
>
> I think I'd actually prefer {enable,disable}_streams in fact.

Hmm, sorry, now I'm confused =). What do you mean with that?

 Tomi