Re: [PATCH v10 2/2] media: rcar-csi2: add Renesas R-Car MIPI CSI-2 receiver driver

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Hi Laurent,

On Sat, Nov 11, 2017 at 08:17:59AM +0200, Laurent Pinchart wrote:
> > > +static int rcar_csi2_s_power(struct v4l2_subdev *sd, int on)
> > > +{
> > > +	struct rcar_csi2 *priv = sd_to_csi2(sd);
> > > +
> > > +	if (on)
> > > +		pm_runtime_get_sync(priv->dev);
> > > +	else
> > > +		pm_runtime_put(priv->dev);
> > 
> > The pipeline you have is already rather complex. Would it be an option to
> > power the hardware on when streaming is started? The smiapp driver does
> > this, without even implementing the s_power callback. (You'd still need to
> > call it on the image source, as long as we have drivers that need it.)
> 
> We've briefly discussed this before, and I agree that pipeline power 
> management needs to be redesigned, but we still haven't agreed on a proper 
> architecture for that. Feel free to propose an RFC :-) In the meantime I 

Well, perhaps we should look at the use cases and see if there are gaps.
Runtime PM is essentially used everywhere else in the kernel.

> wouldn't try to enforce one specific model.

What I just wanted to point out that by switching to runtime PM you avoid
adding a new driver which is dependent on the s_power callback which I
don't think we'll want to keep in the long run. In this case there's no
benefit from s_power in any quantifiable way that I can see.

Actually the master driver manages calling the s_power callback so there's
hardly a need to do so here. It's just that the master drivers still need
that as long as there are sub-device drivers that depend on it.

-- 
Regards,

Sakari Ailus
e-mail: sakari.ailus@xxxxxx
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