linux-kernel - Re: [PATCH v2 4/4] media: tc358746: add Toshiba TC358746 Parallel to CSI-2 bridge driver

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Message-ID: <20220920113524.yq2abqbunvfipnb2@pengutronix.de>
Date:   Tue, 20 Sep 2022 13:35:24 +0200
From:   Marco Felsch <m.felsch@...gutronix.de>
To:     Sakari Ailus <sakari.ailus@...ux.intel.com>
Cc:     Laurent Pinchart <laurent.pinchart@...asonboard.com>,
        mchehab@...nel.org, robh+dt@...nel.org,
        krzysztof.kozlowski+dt@...aro.org, kishon@...com, vkoul@...nel.org,
        hverkuil@...all.nl, jacopo@...ndi.org,
        kieran.bingham+renesas@...asonboard.com,
        linux-media@...r.kernel.org, devicetree@...r.kernel.org,
        linux-kernel@...r.kernel.org, linux-phy@...ts.infradead.org,
        kernel@...gutronix.de
Subject: Re: [PATCH v2 4/4] media: tc358746: add Toshiba TC358746 Parallel to
 CSI-2 bridge driver

On 22-09-19, Sakari Ailus wrote:
> On Mon, Sep 19, 2022 at 03:49:04PM +0300, Laurent Pinchart wrote:
> > On Mon, Sep 19, 2022 at 12:39:35PM +0000, Sakari Ailus wrote:
> > > > +	dev_set_drvdata(dev, tc358746);
> > > > +	pm_runtime_set_autosuspend_delay(dev, 200);
> > > > +	pm_runtime_use_autosuspend(dev);
> > > > +	pm_runtime_enable(dev);
> > > > +
> > > > +	err = tc358746_init_hw(tc358746);
> > > 
> > > The driver depends on runtime PM being enabled but does not depend on
> > > CONFIG_PM. I'd suggest to power the device on and only then enable runtime
> > > PM. See
> > > <URL:https://hverkuil.home.xs4all.nl/spec/driver-api/camera-sensor.html#power-management>.
> > 
> > Or simply depend on CONFIG_PM :-)
> 
> The user can still disable runtime PM.

You mean by user-space? If I read the runtime.c code correctly in such
case the core handles this enabling if one forbid it by increasing the
usage-counter and calling the resume callback. So it is powered as you
want. To fix the PM Kconfig, I will add "depends on PM".

Regards,
  Marco

> I guess few do though. This should be addressed separately from this
> driver, it'd be good to be able to deny that. In fact, no-one has ever
> probably tested this for a large number of drivers and I guess it exists
> just to have a way to disable runtime PM support in drivers that do not
> work with it...
> 
> -- 
> Sakari Ailus
>