linux-kernel - Re: [PATCH 4/6] regulator: lp872x: Add enable GPIO pin support

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Date:	Thu, 31 Dec 2015 22:59:06 +0100
From:	Paul Kocialkowski <contact@...lk.fr>
To:	Mark Brown <broonie@...nel.org>
Cc:	Milo Kim <milo.kim@...com>, linux-kernel@...r.kernel.org,
	Rob Herring <robh+dt@...nel.org>,
	Pawel Moll <pawel.moll@....com>,
	Mark Rutland <mark.rutland@....com>,
	Ian Campbell <ijc+devicetree@...lion.org.uk>,
	Kumar Gala <galak@...eaurora.org>,
	Russell King <linux@....linux.org.uk>,
	Benoît Cousson <bcousson@...libre.com>,
	Tony Lindgren <tony@...mide.com>,
	Liam Girdwood <lgirdwood@...il.com>,
	devicetree@...r.kernel.org, linux-arm-kernel@...ts.infradead.org,
	linux-omap@...r.kernel.org
Subject: Re: [PATCH 4/6] regulator: lp872x: Add enable GPIO pin support

Le jeudi 31 décembre 2015 à 21:40 +0000, Mark Brown a écrit :
> On Wed, Dec 30, 2015 at 07:37:19PM +0100, Paul Kocialkowski wrote:
> > Le mercredi 30 décembre 2015 à 16:33 +0000, Mark Brown a écrit :
> > > On Wed, Dec 30, 2015 at 09:35:21AM +0100, Paul Kocialkowski wrote:
> 
> > > > In my opinion, it would be more elegant to adapt the core regulator
> > > > framework to first enable the GPIO and then call the regulator enable
> > > > ops callback instead of handling the GPIO in the driver.
> 
> > > Why would we want to actively manage both things at runtime?  It's more
> > > work, what do we gain from it?
> 
> > Well, I figured that it would be best to disable the EN pin when we're
> > not using any of the regulators, since that allows the chip to enter
> > standby mode (and thus consume less power).
> 
> This doesn't sound like it's anything to do with the regulators, that's
> a chip wide power management function which should be implemented via
> runtime PM if there's any value in implementing it at all (if the device
> is a primary PMIC normally this would be handled by the CPU core when it
> enters low power state without any software).  It's not something we
> should be considering on a per regulator basis since it's at the chip
> level and on a per regulator basis it's not doing anything useful for
> the reasons above.

I understand, thanks for pointing this out. Well, for my use case, there
is no use in disabling the chip at any point as it powers the external
mmc.

Would you agree to have the enable pin handled directly (and by that, I
mean enabled once, when requested, as I first suggested in the patchset)
in the driver then?

> > It also doesn't hurt regulators that only use a GPIO for enable.
> 
> It causes problems for any device with an optional GPIO,  it means that
> we end up mantaining both GPIO and register which as I've said a couple
> of times now defeats the point of having the GPIO.

Fair enough.

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