linux-kernel - Re: [RFC Patch] gpio: add GPIO hogging mechanism

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Message-ID: <20141029164746.GD21251@lukather>
Date:	Wed, 29 Oct 2014 17:47:46 +0100
From:	Maxime Ripard <maxime.ripard@...e-electrons.com>
To:	Benoit Parrot <bparrot@...com>
Cc:	linus.walleij@...aro.org, linux-gpio@...r.kernel.org,
	linux-kernel@...r.kernel.org, devicetree@...r.kernel.org
Subject: Re: [RFC Patch] gpio: add GPIO hogging mechanism

On Wed, Oct 29, 2014 at 11:41:22AM -0500, Benoit Parrot wrote:
> Maxime Ripard <maxime.ripard@...e-electrons.com> wrote on Wed [2014-Oct-29 11:45:59 +0100]:
> > Hi,
> > 
> > On Tue, Oct 21, 2014 at 03:09:58PM -0500, Benoit Parrot wrote:
> > > Based on Boris Brezillion work this is a reworked patch
> > > of his initial GPIO hogging mechanism.
> > > This patch provides a way to initally configure specific GPIO
> > > when the gpio controller is probe.
> > > 
> > > The actual DT scanning to collect the GPIO specific data is performed
> > > as part of the gpiochip_add().
> > > 
> > > The purpose of this is to allows specific GPIOs to be configured
> > > without any driver specific code.
> > > This particularly usueful because board design are getting
> > > increassingly complex and given SoC pins can now have upward
> > > of 10 mux values a lot of connections are now dependent on
> > > external IO muxes to switch various modes and combination.
> > > 
> > > Specific drivers should not necessarily need to be aware of
> > > what accounts to a specific board implementation. This board level
> > > "description" should be best kept as part of the dts file.
> > > 
> > > Signed-off-by: Benoit Parrot <bparrot@...com>
> > 
> > I've been thinking about this for quite some time, it's good to see
> > some progress on that :)
> > 
> > However, I have a slightly different use case for it: the Allwinner
> > SoCs have a vdd pin coming in for every gpio bank. Nothing out of the
> > ordinary so far, except that some of the boards are using a
> > GPIO-controlled regulator to feed another bank vdd. That obviously
> > causes a chicken-egg issue, since for the gpio-regulator driver to
> > probe, it needs to gpio driver, and for the gpio driver to probe, it
> > needs the regulator driver.
> 
> Unless the gpio controlling the vdd pin is from the same bank your
> trying to power up I do not see the issue here.

Not the same bank, but the same driver.

-- 
Maxime Ripard, Free Electrons
Embedded Linux, Kernel and Android engineering
http://free-electrons.com

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