netdev - Re: [PATCH v2 1/2] PM: runtime: Add a general runtime get sync operation to deal with usage counter

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Message-ID: <CAJZ5v0gGG4FeVfrFOYe1+axv78yh9vA4FAOsbLughbsQosP9-w@mail.gmail.com>
Date:   Mon, 9 Nov 2020 16:20:44 +0100
From:   "Rafael J. Wysocki" <rafael@...nel.org>
To:     Zhang Qilong <zhangqilong3@...wei.com>
Cc:     "Rafael J. Wysocki" <rjw@...ysocki.net>, fugang.duan@....com,
        David Miller <davem@...emloft.net>,
        Jakub Kicinski <kuba@...nel.org>,
        Linux PM <linux-pm@...r.kernel.org>,
        netdev <netdev@...r.kernel.org>
Subject: Re: [PATCH v2 1/2] PM: runtime: Add a general runtime get sync
 operation to deal with usage counter

On Mon, Nov 9, 2020 at 4:00 PM Zhang Qilong <zhangqilong3@...wei.com> wrote:
>
> In many case, we need to check return value of pm_runtime_get_sync, but
> it brings a trouble to the usage counter processing. Many callers forget
> to decrease the usage counter when it failed. It has been discussed a
> lot[0][1]. So we add a function to deal with the usage counter for better
> coding.
>
> [0]https://lkml.org/lkml/2020/6/14/88
> [1]https://patchwork.ozlabs.org/project/linux-tegra/patch/20200520095148.10995-1-dinghao.liu@zju.edu.cn/
> Signed-off-by: Zhang Qilong <zhangqilong3@...wei.com>
> ---
>  include/linux/pm_runtime.h | 30 ++++++++++++++++++++++++++++++
>  1 file changed, 30 insertions(+)
>
> diff --git a/include/linux/pm_runtime.h b/include/linux/pm_runtime.h
> index 4b708f4e8eed..6549ce764400 100644
> --- a/include/linux/pm_runtime.h
> +++ b/include/linux/pm_runtime.h
> @@ -386,6 +386,36 @@ static inline int pm_runtime_get_sync(struct device *dev)
>         return __pm_runtime_resume(dev, RPM_GET_PUT);
>  }
>
> +/**
> + * pm_runtime_general_get - Bump up usage counter of a device and resume it.
> + * @dev: Target device.
> + *
> + * Increase runtime PM usage counter of @dev first, and carry out runtime-resume
> + * of it synchronously. If __pm_runtime_resume return negative value(device is in
> + * error state), we to need decrease the usage counter before it return. If
> + * __pm_runtime_resume return positive value, it means the runtime of device has
> + * already been in active state, and we let the new wrapper return zero instead.
> + *
> + * The possible return values of this function is zero or negative value.
> + * zero:
> + *    - it means resume succeeed or runtime of device has already been active, the
> + *      runtime PM usage counter of @dev remains incremented.
> + * negative:
> + *    - it means failure and the runtime PM usage counter of @dev has been balanced.

The kerneldoc above is kind of noisy and it is hard to figure out what
the helper really does from it.

You could basically say something like "Resume @dev synchronously and
if that is successful, increment its runtime PM usage counter.  Return
0 if the runtime PM usage counter of @dev has been incremented or a
negative error code otherwise."

> + */
> +static inline int pm_runtime_general_get(struct device *dev)

What about pm_runtime_resume_and_get()?

> +{
> +       int ret = 0;

This extra initialization is not necessary.

You can initialize ret to the __pm_runtime_resume() return value right away.

> +
> +       ret = __pm_runtime_resume(dev, RPM_GET_PUT);
> +       if (ret < 0) {
> +               pm_runtime_put_noidle(dev);
> +               return ret;
> +       }
> +
> +       return 0;
> +}
> +
>  /**
>   * pm_runtime_put - Drop device usage counter and queue up "idle check" if 0.
>   * @dev: Target device.
> --