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

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Message-ID: <4a2cb923ab264d7d99107a450d6ddcba@BN1BFFO11FD057.protection.gbl>
Date:	Fri, 31 Oct 2014 10:40:42 -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 06:36PM +0100, Linus Walleij wrote:
> On Fri, Oct 31, 2014 at 5:57 PM, Sören Brinkmann
> <soren.brinkmann@...inx.com> wrote:
> > On Fri, 2014-10-31 at 09:17AM +0100, Linus Walleij wrote:
> 
> >> 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 was more thinking as everything you don't enable explicitly
> in a state is per definition disabled.
> 
> So if you are in state A and tri-state is enabled there and you
> move to state B where pull-up is enabled, then tri-state should
> be disabled, since it is not explicitly enabled.
> 
> > 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.
> 
> Well look at the callback from the core:
> 
>         int (*pin_config_set) (struct pinctrl_dev *pctldev,
>                                unsigned pin,
>                                unsigned long *configs,
>                                unsigned num_configs);
> 
> You get all configs in an array. The driver can walk over the list and
> make informed decisions on what to do *BEFORE* poking any registers.
> 
> Avoiding transients as you describe is part of why the callback
> looks as it does. This is why every driver has its own for-loop.

Okay, I guess that is possible. I find usage of the arguments more
elegant since it is more explicit and reduces code in the driver, but I
suspect it should work.

	Thanks,
	Sören
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