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

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Message-ID: <1401435691.13544.3.camel@iivanov-dev>
Date:	Fri, 30 May 2014 10:41:31 +0300
From:	"Ivan T. Ivanov" <iivanov@...sol.com>
To:	Linus Walleij <linus.walleij@...aro.org>
Cc:	Heiko Stübner <heiko@...ech.de>,
	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, 2014-05-28 at 10:48 +0200, Linus Walleij wrote:
> 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.
> 

In my case this is just a switch, which can select from different power
sources and these sources are external from the chip. So I can't know
a priory what the levels are and hard code them inside the driver.

Thanks,
Ivan


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