linux-kernel - Re: [RFC PATCH] pinctrl-single: Use of pinctrl-single for external device over I2C

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Date:	Thu, 16 Jul 2015 14:58:13 +0200
From:	Linus Walleij <linus.walleij@...aro.org>
To:	Vaibhav Hiremath <vaibhav.hiremath@...aro.org>
Cc:	"linux-arm-kernel@...ts.infradead.org" 
	<linux-arm-kernel@...ts.infradead.org>,
	Rob Herring <robh+dt@...nel.org>,
	Lee Jones <lee.jones@...aro.org>,
	Will Deacon <will.deacon@....com>,
	Tony Lindgren <tony@...mide.com>,
	"devicetree@...r.kernel.org" <devicetree@...r.kernel.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	"linux-gpio@...r.kernel.org" <linux-gpio@...r.kernel.org>
Subject: Re: [RFC PATCH] pinctrl-single: Use of pinctrl-single for external
 device over I2C

On Thu, Jul 2, 2015 at 6:53 PM, Vaibhav Hiremath
<vaibhav.hiremath@...aro.org> wrote:

> In some usecases, the external device (in my case it PMIC over I2C)
> does support pin in multiple configuration, we may need to control/configure them
> during boot or runtime.

What is missing from this patch is an explanation why pinctrl-single should
be used for this PMIC.

Repeat: pinctrl-single: when you have exactly one register per pin, and
the description of the pins is delivered in an opaque ASIC-specific format
without developers knowing much about how the hardware actually works,
just "set these magic values".

I strongly prefer that this PMIC has its own pin controller using standard
bindings with groups and functions, see eg. drivers/pinctrl/nomadik/pinctrl-ab*
for a PMIC pinctrl driver.

Yours,
Linus Walleij
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