linux-kernel - Re: [PATCH RFC v2 8/8] ARM: zynq: DT: Add pinctrl information

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Message-ID: <030ed753d9764825b1bd5c845b360c7d@BN1AFFO11FD036.protection.gbl>
Date:	Fri, 31 Oct 2014 09:57:43 -0700
From:	Sören Brinkmann <soren.brinkmann@...inx.com>
To:	Linus Walleij <linus.walleij@...aro.org>
CC:	Michal Simek <michal.simek@...inx.com>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	"linux-arm-kernel@...ts.infradead.org" 
	<linux-arm-kernel@...ts.infradead.org>,
	Steffen Trumtrar <s.trumtrar@...gutronix.de>
Subject: Re: [PATCH RFC v2 8/8] ARM: zynq: DT: Add pinctrl information

On Fri, 2014-10-31 at 09:17AM +0100, Linus Walleij wrote:
> On Tue, Oct 28, 2014 at 5:03 PM, Sören Brinkmann
> <soren.brinkmann@...inx.com> wrote:
> > On Tue, 2014-10-28 at 04:05PM +0100, Linus Walleij wrote:
> >> On Thu, Oct 16, 2014 at 7:11 PM, Soren Brinkmann
> >> <soren.brinkmann@...inx.com> wrote:
> >>
> >> > Add pinctrl descriptions to the zc702 and zc706 device trees.
> >> >
> >> > Signed-off-by: Soren Brinkmann <soren.brinkmann@...inx.com>
> >>
> >> (...)
> >> > +&pinctrl0 {
> >> > +       pinctrl_can0_default: pinctrl-can0-default {
> >> > +               common {
> >> > +                       function = "can0";
> >> > +                       groups = "can0_9_grp";
> >> > +                       bias-pull-up = <0>;
> >>
> >> No. If you want pull-up, just use
> >> bias-pull-up;
> >>
> >> If you want to disable pull-up, use
> >> bias-disable;
> >
> > But bias-disable also disables high-impedance. That doesn't work for me,
> > I think.
> 
> Hm. Some sequencing problem right? Like you count on
> bias-high-impdedance being set in some other state?
> 
> I think each state should be self-contained, so you set
> all the stuff you need in a state, do not rely on things coming
> in pre-set from another state.
> 
> So in this case just set bias-high-impedance; then and
> if the state does not have bias-pull-up, *always* disable it
> in the driver.
> 
> >>
> >> > +                       slew-rate = <0>;
> >>
> >> If this measure is any kind of time unit, this is against the laws of nature.
> >
> > It's not. As the bindings say, the argument is driver specific.
> 
> Okay then.
> 
> >> > +               rx {
> >> > +                       pins = "MIO46";
> >> > +                       bias-high-impedance = <1>;
> >>
> >> Just
> >> bias-high-impedance;
> >
> > Same problem as I have above. To allow all permutations of pull-up and
> > tri-state I can't just have a single disable-bias property.
> 
> Again it seems to be a sequencing problem. And device tree is
> not good at sequences, therefore all states should be self-contained.

I agree, but how would I define a pin with pull-up enabled and
tri-state disabled - assume the pin is currently in a random state that
can have those things set/not set arbitrarily.

I don't see how that can be handled without using arguments the way I
proposed.

I can't put bias-disable in DT since it would potentially disable both
and the pull-up enable would have only a transient effect.
I can't do the sequencing in the driver either. If I see pull-up enable,
I can't imply an effect on tri-state since I can't know whether there
was/will be a tri-state property that sets it as well.

	Sören
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