linux-kernel - Re: [PATCH v2 2/2] pinctrl: Allow indicating loss of pin states during low-power

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Message-ID: <CACRpkdbFHj9pM6R3azVPKgbQ-LMmitEdJHQ5BOEb7Vy=kpNk4A@mail.gmail.com>
Date:   Sat, 2 Dec 2017 13:48:14 +0100
From:   Linus Walleij <linus.walleij@...aro.org>
To:     Florian Fainelli <f.fainelli@...il.com>
Cc:     Tony Lindgren <tony@...mide.com>, linux-gpio@...r.kernel.org,
        Rob Herring <robh+dt@...nel.org>,
        Mark Rutland <mark.rutland@....com>,
        "open list:OPEN FIRMWARE AND FLATTENED DEVICE TREE BINDINGS" 
        <devicetree@...r.kernel.org>,
        open list <linux-kernel@...r.kernel.org>,
        Charles Keepax <ckeepax@...nsource.cirrus.com>,
        Charles Keepax <ckeepax@...nsource.wolfsonmicro.com>,
        Stephen Warren <swarren@...dia.com>,
        Andy Shevchenko <andy.shevchenko@...il.com>,
        Al Cooper <alcooperx@...il.com>,
        bcm-kernel-feedback-list <bcm-kernel-feedback-list@...adcom.com>
Subject: Re: [PATCH v2 2/2] pinctrl: Allow indicating loss of pin states
 during low-power

On Wed, Nov 29, 2017 at 6:37 PM, Florian Fainelli <f.fainelli@...il.com> wrote:
> On 11/29/2017 09:02 AM, Tony Lindgren wrote:

>> Hmm well typically a device driver that loses it's context just does
>> save and restore of the registers in runtime PM suspend/resume
>> as needed. In this case it would mean duplicating the state for
>> potentially for hundreds of registers.. So using the existing
>> state in the pinctrl subsystem totally makes sense for the pins.
>>
>> Florian do you have other reasons why this should be done in the
>> pinctrl framework instead of the driver? Might be worth describing
>> the reasoning in the patch descriptions :)
>
> The pinctrl provider driver that I am using is pinctrl-single, which has
> proper suspend/resume callbacks but those are not causing any HW
> programming to happen because of the (p->state == state) check, hence
> this patch series.

So we are talking about these callbacks, correct?

#ifdef CONFIG_PM
static int pinctrl_single_suspend(struct platform_device *pdev,
                                        pm_message_t state)
{
        struct pcs_device *pcs;

        pcs = platform_get_drvdata(pdev);
        if (!pcs)
                return -EINVAL;

        return pinctrl_force_sleep(pcs->pctl);
}

static int pinctrl_single_resume(struct platform_device *pdev)
{
        struct pcs_device *pcs;

        pcs = platform_get_drvdata(pdev);
        if (!pcs)
                return -EINVAL;

        return pinctrl_force_default(pcs->pctl);
}
#endif

Which falls through to this:

/**
 * pinctrl_force_sleep() - turn a given controller device into sleep state
 * @pctldev: pin controller device
 */
int pinctrl_force_sleep(struct pinctrl_dev *pctldev)
{
        if (!IS_ERR(pctldev->p) && !IS_ERR(pctldev->hog_sleep))
                return pinctrl_select_state(pctldev->p, pctldev->hog_sleep);
        return 0;
}
EXPORT_SYMBOL_GPL(pinctrl_force_sleep);

/**
 * pinctrl_force_default() - turn a given controller device into default state
 * @pctldev: pin controller device
 */
int pinctrl_force_default(struct pinctrl_dev *pctldev)
{
        if (!IS_ERR(pctldev->p) && !IS_ERR(pctldev->hog_default))
                return pinctrl_select_state(pctldev->p, pctldev->hog_default);
        return 0;
}
EXPORT_SYMBOL_GPL(pinctrl_force_default);

So am I right in assuming it is actually the hogs that is your biggest
problem, and those are the states that get lost over suspend/resume
that are especially problematic?

I.e. you don't have any problem with any non-hogged pinctrl
handles, those are handled just fine in the suspend/resume
paths of the client drivers?

If this is the case, it changes the problem scope slightly.

It is fair that functions named *force* should actually enforce
programming a state.

So then I would suggest somethin else: break pinctrl_select_state()
into two:

pinctrl_select_state() that works just like before, checking if
(p->state == state) but which calls a static function
pinctrl_select_state_commit() that commits the change unconditonally.
Then alter pinctrl_force_sleep() and pinctrl_force_sleep() to call
that function.

This should solve your problem without having to alter the semantics
of pinctrl_select_state() for everyone.

If you want I can cook a patch to illustrate what I mean so you can
try it.

Yours,
Linus Walleij