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

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Date:   Mon, 9 Nov 2020 13:59:51 +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 1/2] PM: runtime: Add a general runtime get sync operation
 to deal with usage counter

On Mon, Nov 9, 2020 at 9:05 AM 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 | 32 ++++++++++++++++++++++++++++++++
>  1 file changed, 32 insertions(+)
>
> diff --git a/include/linux/pm_runtime.h b/include/linux/pm_runtime.h
> index 4b708f4e8eed..2b0af5b1dffd 100644
> --- a/include/linux/pm_runtime.h
> +++ b/include/linux/pm_runtime.h
> @@ -386,6 +386,38 @@ static inline int pm_runtime_get_sync(struct device *dev)
>         return __pm_runtime_resume(dev, RPM_GET_PUT);
>  }
>
> +/**
> + * gene_pm_runtime_get_sync - Bump up usage counter of a device and resume it.
> + * @dev: Target device.

The force argument is not documented.

> + *
> + * 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) or return positive value(the runtime of device is already active)
> + * with force is true, it need decrease the usage counter of the device when
> + * return.
> + *
> + * The possible return values of this function is zero or negative value.
> + * zero:
> + *    - it means success and the status will store the resume operation status
> + *      if needed, the runtime PM usage counter of @dev remains incremented.
> + * negative:
> + *    - it means failure and the runtime PM usage counter of @dev has been
> + *      decreased.
> + * positive:
> + *    - it means the runtime of the device is already active before that. If
> + *      caller set force to true, we still need to decrease the usage counter.

Why is this needed?

> + */
> +static inline int gene_pm_runtime_get_sync(struct device *dev, bool force)

The name is not really a good one and note that pm_runtime_get() has
the same problem as _get_sync() (ie. the usage counter is incremented
regardless of the return value).

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

Thanks!