linux-kernel - Re: [RFC PATCH] drivers/pinctrl: Add the concept of an "init" state

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Message-ID: <20141008134615.GA6586@kroah.com>
Date:	Wed, 8 Oct 2014 06:46:15 -0700
From:	Greg KH <gregkh@...uxfoundation.org>
To:	Linus Walleij <linus.walleij@...aro.org>
Cc:	Doug Anderson <dianders@...omium.org>,
	Thierry Reding <thierry.reding@...il.com>,
	Mark Brown <broonie@...nel.org>,
	Lee Jones <lee.jones@...aro.org>,
	Chris Zhong <zyw@...k-chips.com>,
	Heiko Stuebner <heiko@...ech.de>,
	Sonny Rao <sonnyrao@...omium.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: Re: [RFC PATCH] drivers/pinctrl: Add the concept of an "init" state

On Wed, Oct 08, 2014 at 11:00:11AM +0200, Linus Walleij wrote:
> On Tue, Oct 7, 2014 at 10:28 PM, Doug Anderson <dianders@...omium.org> wrote:
> 
> > For pinctrl the "default" state is applied to pins before the driver's
> > probe function is called.  This is normally a sensible thing to do,
> > but in some cases can cause problems.  That's because the pins will
> > change state before the driver is given a chance to program how those
> > pins should behave.
> >
> > As an example you might have a regulator that is controlled by a PWM
> > (output high = high voltage, output low = low voltage).  The firmware
> > might leave this pin as driven high.  If we allow the driver core to
> > reconfigure this pin as a PWM pin before the PWM's probe function runs
> > then you might end up running at too low of a voltage while we probe.
> >
> > Let's introudce a new "init" state.  If this is defined we'll set
> > pinctrl to this state before probe and then "default" after probe
> > (unless the driver explicitly changed states already).
> >
> > An alternative idea that was thought of was to use the pre-existing
> > "sleep" or "idle" states and add a boolean property that we should
> > start in that mode.  This was not done because the "init" state is
> > needed for correctness and those other states are only present (and
> > only transitioned in to and out of) when (optional) power management
> > is enabled.
> >
> > Signed-off-by: Doug Anderson <dianders@...omium.org>
> 
> I *like* this approach. A lot.
> 
> It will come with DT bindings for free as it's just strings.
> 
> > +++ b/drivers/base/dd.c
> > @@ -308,6 +308,8 @@ static int really_probe(struct device *dev, struct device_driver *drv)
> >                         goto probe_failed;
> >         }
> >
> > +       pinctrl_init_done(dev);
> 
> We will need Greg's ACK for this oneliner.

As much as I hate subsystem-specific code in the driver core, I guess I
let this happen before, so I can't object here :)

Acked-by: Greg Kroah-Hartman <gregkh@...uxfoundation.org>
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