linux-kernel - Re: [PATCH v2] pinctrl: Enable "power-source" to be extracted from DT files

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Message-ID: <CACRpkdYR9cZOnG2r3Kh027LNKgsDJqxL0J9Gryu+JHXacTNHbQ@mail.gmail.com>
Date:	Wed, 28 May 2014 10:48:11 +0200
From:	Linus Walleij <linus.walleij@...aro.org>
To:	Heiko Stübner <heiko@...ech.de>
Cc:	"Ivan T. Ivanov" <iivanov@...sol.com>,
	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>,
	Randy Dunlap <rdunlap@...radead.org>,
	James Hogan <james.hogan@...tec.com>,
	Stephen Warren <swarren@...dia.com>,
	"devicetree@...r.kernel.org" <devicetree@...r.kernel.org>,
	"linux-doc@...r.kernel.org" <linux-doc@...r.kernel.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH v2] pinctrl: Enable "power-source" to be extracted from DT files

On Wed, May 28, 2014 at 10:36 AM, Heiko Stübner <heiko@...ech.de> wrote:
> Am Mittwoch, 28. Mai 2014, 10:15:43 schrieb Linus Walleij:
>> On Tue, May 27, 2014 at 3:09 PM, Heiko Stübner <heiko@...ech.de> wrote:
>> > Am Dienstag, 27. Mai 2014, 09:27:36 schrieb Ivan T. Ivanov:
>> >> From: "Ivan T. Ivanov" <iivanov@...sol.com>
>> >>
>> >> Add "power-source" property to generic options used for DT parsing files.
>> >> This  enables drivers, which use generic pin configurations, to get the
>> >> value passed to this property.
>> >
>> > I think the main problem here is, that pinconf-generic.h defines the
>> > power-
>> > source as having a "custom format". With DT as a hardware description,
>> > implementaton specific values do not work well - instead it should have a
>> > regular unit-value.
>> >
>> > For the power-source I think volts could work well - as this is the main
>> > use- case for pinctrl I know. The regulator-binding uses microvolts,
>> > maybe it would be good use a similar unit.
>>
>> (...)
>>
>> >         pcfg_1v8 {
>> >
>> >                 power-source = <1800000>;
>> >
>> >         };
>>
>> I don't think this is what it's meant for actually. In this case the thing
>> would be modeled as a regulator rather than some pin control option I
>> guess?
>>
>> I think it's more like a selector, such as found on old amplifiers,
>> input source A, B or C? So it's just some discrete number.
>
> as I said, you know this better than me ;-)
>
> I was thinking more of these io-voltages, where one can select between say 1.8
> and 3.3V for the pins.
>
> I have this somewhere on my todo list for the rockchips too.
>
> So essentially the pinctrl driver [as it is a pin-group specific setting]
> should just export regulators for these voltage settings, without touching the
> pinconfig itself, right?

Hm hm hm.

I am a bit in the blue actually.

I think we need to have a discussion with Mark Brown on how to
handle this.

We have previously had the case of MMC/SD level-shifters, where
a certain setting gives a certain level of signals out, and another setting
gives another level. Like two discrete levels.

So we modeled that as a regulator provider inside the pin control
driver eventually, see sh-pfc/pfc-sh73a0.c

But this is different: it is the power of the pin itself.

I can think of a "padring regulator" hooking in as part of the pin state
but have no clear idea on how to actually do that. We need some
coding I think.

Yours,
Linus Walleij
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