linux-kernel - Re: [PATCH 3/4] pinctrl: Add support for additional dynamic states

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Message-ID: <20130719072927.GY7656@atomide.com>
Date:	Fri, 19 Jul 2013 00:29:27 -0700
From:	Tony Lindgren <tony@...mide.com>
To:	Stephen Warren <swarren@...dotorg.org>
Cc:	linus.walleij@...aro.org, linux-omap@...r.kernel.org,
	linux-kernel@...r.kernel.org, linux-arm-kernel@...ts.infradead.org
Subject: Re: [PATCH 3/4] pinctrl: Add support for additional dynamic states

* Stephen Warren <swarren@...dotorg.org> [130718 12:27]:
> On 07/18/2013 01:25 AM, Tony Lindgren wrote:
> > * Stephen Warren <swarren@...dotorg.org> [130717 14:21]:
> >> On 07/16/2013 03:05 AM, Tony Lindgren wrote:
> >>> To toggle dynamic states, let's add the optional active state in
> >>> addition to the static default state. Then if the optional active
> >>> state is defined, we can require that idle and sleep states cover
> >>> the same pingroups as the active state.
> >>>
> >>> Then let's add pinctrl_check_dynamic() and pinctrl_select_dynamic()
> >>> to use instead of pinctrl_select() to avoid breaking existing users.
> >>>
> >>> With pinctrl_check_dynamic() we can check that idle and sleep states
> >>> match the active state for pingroups during init, and don't need to
> >>> do it during runtime.
> >>>
> >>> Then with the states pre-validated, pinctrl_select_dynamic() can
> >>> just toggle between the dynamic states without extra checks.
> >>>
> >>> Note that pinctr_select_state() still has valid use cases, such as
> >>> changing states when the pins can be shared between two drivers
> >>> and don't necessarily cover the same pingroups. For dynamic runtime
> >>> toggling of pin states, we should eventually always use just
> >>> pinctrl_select_dynamic().
> 
> >>> @@ -1241,7 +1371,13 @@ static int pinctrl_pm_select_state(struct device *dev, struct pinctrl_state *sta
> >>>  		return 0;
> >>>  	if (IS_ERR(state))
> >>>  		return 0; /* No such state */
> >>> -	ret = pinctrl_select_state(pins->p, state);
> >>> +
> >>> +	/* Configured for proper dynamic muxing? */
> >>> +	if (!IS_ERR(dev->pins->active_state))
> >>> +		ret = pinctrl_select_dynamic(pins->p, state);
> >>> +	else
> >>> +		ret = pinctrl_select_state(pins->p, state);
> >>
> >> Hmmm. I'm not quite sure this is right... Surely this function should
> >> just do nothing if the dynamic states aren't defined? The system should
> >> just, and only, be in the "default" state and never do anything else.
> > 
> > This keeps the existing behaviour. We should be able to drop the
> > call to pinctrl_select_state() here after the existing use in
> > drivers has been fixed.
> 
> How many DT-based systems already have multiple of default/idle/sleep
> states defined in DT? Right now, since the kernel code uses
> pinctrl_select_state() to switch between those, the state definitions
> need to define /all/ pins used by those states, not just the dynamic
> ones. However, with this series in place, the default state should only
> include the static pins, and the active/idle/sleep states should only
> include the dynamic pins. That's a change to the DT bindings, since it
> changes how the DT must be written, and causes older DTs to be
> incompatible with newer kernels and vice-versa.

Well we can keep the current behaviour with pinctrl_select_state() around
as long as needed. For the legacy cases, there is no active state defined
and we fall back to pinctrl_select_state().
 
> So, do we just ignore this DT ABI change again, or insist on doing it in
> some compatible way? DT ABI-ness is a PITA:-(

I'd vote for keeping the existing behaviour with pinctrl_select_state()
when no active state is defined.

Regards,

Tony

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