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

["Heiko Stübner" <heiko@sntech.de>]

Am Freitag, 30. Mai 2014, 10:41:31 schrieb Ivan T. Ivanov:
> On Wed, 2014-05-28 at 10:48 +0200, Linus Walleij wrote:
> > On Wed, May 28, 2014 at 10:36 AM, Heiko Stübner <heiko@sntech.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@sntech.de> wrote:
> > >> > Am Dienstag, 27. Mai 2014, 09:27:36 schrieb Ivan T. Ivanov:
> > >> >> From: "Ivan T. Ivanov" <iivanov@mm-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.

Yep, that is exactly what Linus described as use-case too ... I was simply 
thinking in the wrong direction :-)

Heiko