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

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Message-ID: <51E8401E.8040705@wwwdotorg.org>
Date:	Thu, 18 Jul 2013 13:21:02 -0600
From:	Stephen Warren <swarren@...dotorg.org>
To:	Tony Lindgren <tony@...mide.com>
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

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.

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:-(
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