Re: [RFC 4/5] media: i2c: max9286: Fetch PIXEL_RATE in s_stream

[Jacopo Mondi <jacopo@jmondi.org>]

Hi Laurent,

On Mon, Aug 23, 2021 at 05:17:05AM +0300, Laurent Pinchart wrote:
> Hi Jacopo,
>
> Thank you for the patch.
>
> On Tue, Aug 17, 2021 at 09:27:02AM +0200, Jacopo Mondi wrote:
> > The max9286 driver needs to fetch the remote serializer PIXEL_RATE
> > control value in order to compute its own one, as the sum of the
>
> s/its own one/its own/ (or its own pixel rate)
>
> > values reported by the connected subdevices.
> >
> > Currently the control is verified to be present at notifier's bound
> > time, which requires the serializer driver to register the control at
> > probe time. As the serializer driver might need to register the control
> > later, by adding the control handler of its connected sensor, post-pone
> > the max9286 check for the control availability at start stream time.
> >
> > Signed-off-by: Jacopo Mondi <jacopo+renesas@jmondi.org>
> > ---
> >  drivers/media/i2c/max9286.c | 6 +++++-
> >  1 file changed, 5 insertions(+), 1 deletion(-)
> >
> > diff --git a/drivers/media/i2c/max9286.c b/drivers/media/i2c/max9286.c
> > index 1b92d18a1f94..98fc90339a9e 100644
> > --- a/drivers/media/i2c/max9286.c
> > +++ b/drivers/media/i2c/max9286.c
> > @@ -595,7 +595,7 @@ static int max9286_notify_bound(struct v4l2_async_notifier *notifier,
> >  	max9286_check_config_link(priv, priv->source_mask);
> >  	max9286_configure_i2c(priv, false);
> >
> > -	return max9286_set_pixelrate(priv);
> > +	return 0;
> >  }
> >
> >  static void max9286_notify_unbind(struct v4l2_async_notifier *notifier,
> > @@ -674,6 +674,10 @@ static int max9286_s_stream(struct v4l2_subdev *sd, int enable)
> >  	int ret;
> >
> >  	if (enable) {
> > +		ret = max9286_set_pixelrate(priv);
> > +		if (ret)
> > +			return ret;
>
> That's very likely not going to work. The CSI-2 receiver connected to
> the max9286 will need to know the pixel rate as part of its
> initialization sequence, before calling .s_stream(1) on the max9286.
>

How so ? The R-Car CSI-2 receiver feteches the pixel rate at s_stream
time, I thought it was customary to do so. What is it needed for before
streamon time ?

> > +
> >  		/*
> >  		 * The frame sync between cameras is transmitted across the
> >  		 * reverse channel as GPIO. We must open all channels while
>
> --
> Regards,
>
> Laurent Pinchart