linux-kernel - Re: [PATCH V4 4/5] gpio: gpio-xilinx: Add support for suspend and resume

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Date:   Thu, 7 Jan 2021 10:46:51 +0100
From:   Linus Walleij <linus.walleij@...aro.org>
To:     Srinivas Neeli <srinivas.neeli@...inx.com>
Cc:     Bartosz Golaszewski <bgolaszewski@...libre.com>,
        Michal Simek <michal.simek@...inx.com>,
        Shubhrajyoti Datta <shubhrajyoti.datta@...inx.com>,
        sgoud@...inx.com, Robert Hancock <hancock@...systems.ca>,
        William Breathitt Gray <vilhelm.gray@...il.com>,
        Syed Nayyar Waris <syednwaris@...il.com>,
        "open list:GPIO SUBSYSTEM" <linux-gpio@...r.kernel.org>,
        Linux ARM <linux-arm-kernel@...ts.infradead.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        git@...inx.com
Subject: Re: [PATCH V4 4/5] gpio: gpio-xilinx: Add support for suspend and resume

On Wed, Jan 6, 2021 at 1:27 PM Srinivas Neeli <srinivas.neeli@...inx.com> wrote:

> Add support for suspend and resume, pm runtime suspend and resume.
> Added free and request calls.
>
> Signed-off-by: Srinivas Neeli <srinivas.neeli@...inx.com>
(...)

> +static int xgpio_request(struct gpio_chip *chip, unsigned int offset)
> +{
> +       int ret;
> +
> +       ret = pm_runtime_get_sync(chip->parent);
> +       /*
> +        * If the device is already active pm_runtime_get() will return 1 on
> +        * success, but gpio_request still needs to return 0.
> +        */
> +       return ret < 0 ? ret : 0;
> +}

That's clever. I think more GPIO drivers should be doing it like this,
today I think most just ignore the return code.

> +static int __maybe_unused xgpio_suspend(struct device *dev)
> +static int __maybe_unused xgpio_resume(struct device *dev)

Those look good.


>  /**
>   * xgpio_remove - Remove method for the GPIO device.
>   * @pdev: pointer to the platform device
> @@ -289,7 +323,10 @@ static int xgpio_remove(struct platform_device *pdev)
>  {
>         struct xgpio_instance *gpio = platform_get_drvdata(pdev);
>
> -       clk_disable_unprepare(gpio->clk);
> +       if (!pm_runtime_suspended(&pdev->dev))
> +               clk_disable_unprepare(gpio->clk);
> +
> +       pm_runtime_disable(&pdev->dev);

This looks complex and racy. What if the device is resumed after you
executed the
first part of the statement.

The normal sequence is:

pm_runtime_get_sync(dev);
pm_runtime_put_noidle(dev);
pm_runtime_disable(dev);

This will make sure the clock is enabled and pm runtime is disabled.
After this you can unconditionally call clk_disable_unprepare(gpio->clk);

It is what you are doing on the errorpath of probe().

Yours,
Linus Walleij