linux-kernel - Re: [PATCHv2] Input: omap4-keypad: Add pinctrl support

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Date:	Wed, 24 Oct 2012 19:57:49 +0300
From:	Felipe Balbi <balbi@...com>
To:	Dmitry Torokhov <dmitry.torokhov@...il.com>
CC:	Linus Walleij <linus.walleij@...aro.org>,
	Benoit Cousson <b-cousson@...com>,
	Sourav Poddar <sourav.poddar@...com>, <tony@...mide.com>,
	<linux-omap@...r.kernel.org>, <linux-kernel@...r.kernel.org>,
	<devicetree-discuss@...ts.ozlabs.org>,
	<linux-arm-kernel@...ts.infradead.org>,
	<linux-input@...r.kernel.org>, Felipe Balbi <balbi@...com>
Subject: Re: [PATCHv2] Input: omap4-keypad: Add pinctrl support

Hi,

On Wed, Oct 24, 2012 at 09:18:01AM -0700, Dmitry Torokhov wrote:
> On Wed, Oct 24, 2012 at 02:54:23PM +0200, Linus Walleij wrote:
> > On Tue, Oct 23, 2012 at 10:02 PM, Dmitry Torokhov
> > <dmitry.torokhov@...il.com> wrote:
> > 
> > > I have seen just in a few days 3 or 4 drivers having exactly the same
> > > change - call to devm_pinctrl_get_select_default(), and I guess I will
> > > receive the same patches for the rest of input drivers shortly.
> > > This suggests that the operation is done at the wrong level. Do the
> > > pin configuration as you parse DT data, the same way you set up i2c
> > > devices registers in of_i2c.c, and leave the individual drivers that do
> > > not care about specifics alone.
> > 
> > Exactly this can be done with pinctrl hogs.
> > 
> > The problem with that is that it removes the cross-reference
> > between the device and it's pinctrl handle (also from the device
> > tree). Instead the pinctrl handle gets referenced to the pin controller
> > itself. So from a modelling perpective this looks a bit ugly.
> > 
> > So we have two kinds of ugly:
> > 
> > - Sprinke devm_pinctrl_get_select_default() over all drivers
> >   which makes pinctrl handles properly reference their devices
> > 
> > - Use hogs and loose coupling between pinctrl handles and their
> >   devices
> > 
> > A third alternative as outlined is to use notifiers and some
> > resource core in drivers/base/*
> 
> OK, so with drivers/base/, have you considered doing default pinctrl
> selection in bus's probe() methods? Yo would select the default
> configuration before starting probing the device and maybe select idle
> when probe fails or device is unbound? That would still keep the link
> between device object and pinctrl and there less busses than device
> drivers out there.

it starts to become confusing after a while. I mean, there's a reason
why all drivers explictly call pm_runtim_enable(), right ?

From a first thought, one could think of just yanking that into bus'
probe() as you may suggest, but sometimes the device is already enabled,
so we need extra tricks:

pm_runtime_set_active();
pm_runtime_enable();
pm_runtime_get();

the same could happen with pinctrl eventually. What if a device needs to
do something else (an errata fix as an example) before requesting
pinctrl's default state ?

-- 
balbi

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