linux-kernel - Re: [PATCH] pinctrl: Really force states during suspend/resume

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Message-ID: <CAHp75Vcn6sc5XtgcT4zhVQ=9UgB6KsrLaXjPBsi_9jfpm3Vwfw@mail.gmail.com>
Date:   Tue, 28 Feb 2017 00:53:44 +0200
From:   Andy Shevchenko <andy.shevchenko@...il.com>
To:     Linus Walleij <linus.walleij@...aro.org>
Cc:     Ulf Hansson <ulf.hansson@...aro.org>,
        Florian Fainelli <f.fainelli@...il.com>,
        Al Cooper <alcooperx@...il.com>,
        Stephen Warren <swarren@...dia.com>,
        "open list:PIN CONTROL SUBSYSTEM" <linux-gpio@...r.kernel.org>,
        open list <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH] pinctrl: Really force states during suspend/resume

On Thu, Feb 23, 2017 at 12:30 PM, Linus Walleij
<linus.walleij@...aro.org> wrote:
> On Wed, Feb 8, 2017 at 10:46 PM, Andy Shevchenko
> <andy.shevchenko@...il.com> wrote:
>
>> Btw, I have got similar issue and thinking about those states they are
>> quite orthogonal to the pin states. Wouldn't be better to actually
>> differentiate PM related states and pin states?
>
> I don't fully understand what you mean here, but I like the sound
> of it.
>
> "sleep" and "default" were traditionally related to the system
> suspend/resume states. It was suggested that the core handle this
> automatically, but it doesn't work because of things like that
> userspace can disable a TTY/UART and then it should sleep,
> regardless of the state of the system.
>
> Runtime PM "sleep" and "resume" is closer to what we want to
> achieve here, and might be a good integration point.
> (CC:ing Ulf, he's looking into things like this.)

Yeah, so, what I meant is that pinctrl so called "states" are so
abstract and PM related that:

- doesn't allow clearly integrate them to ACPI (I suppose we will get
support of pin configuration and pin muxing support in ACPI
officially)

- requires too many explicit calls and hacks to make it work in more
or less standard cases (for example, when we request GPIO in ->probe()
solely to get a wake capable source, which requires to have defined 3
states instead of 2 or a hack, because pinctrl design checks for state
change during ->probe() and applies "default" if and only if there
were defined "default" state, meaning additional burden on definitions
in hardware pin control driver).

I hope it makes picture a bit clearer.

>> In my case I have a ->probe() function where device is requested GPIO
>> in order to make it wake capable source without using anywhere else.
>> So, this requires to have "init" state to be defined which is kinda
>> inconvenient.
>>
>> On resume/suspend it calls pinctrl_pm_state*() and requires "default"
>> and "sleep" states to be defined.
>>
>> I think GPIO case is quite generic and pin control framework lacks of
>> something like switching some pins of the group to GPIO state and back
>> whenever they defined as wake capable sources.
>
> I guess by "GPIO state" you are referring to what is discussed in
> Documentation/pinctrl.txt as "GPIO mode pitfalls", i.e. it is not really
> used as a GPIO, but as part of a device functionality it just happens
> that the TRM calls the asynchronous (low power mode) edge detector
> mode "GPIO".

Yes.

>> I would work towards fixing this issue anyway (to get UART runtime PM
>> working on serial consoles).
>
> Everyone would be grateful for that.

Please, check latest ACPI drafts you have access to.

-- 
With Best Regards,
Andy Shevchenko