linux-kernel - Re: [PATCH][v3] mfd: intel-lpss: Avoid resuming runtime-suspended lpss unnecessarily

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Date:   Fri, 30 Sep 2016 02:14:31 +0200
From:   "Rafael J. Wysocki" <rafael@...nel.org>
To:     Chen Yu <yu.c.chen@...el.com>, Lee Jones <lee.jones@...aro.org>
Cc:     Linux PM <linux-pm@...r.kernel.org>, Pavel Machek <pavel@....cz>,
        Len Brown <len.brown@...el.com>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        Andy Shevchenko <andriy.shevchenko@...ux.intel.com>,
        Mika Westerberg <mika.westerberg@...ux.intel.com>,
        "Rafael J . Wysocki" <rafael.j.wysocki@...el.com>
Subject: Re: [PATCH][v3] mfd: intel-lpss: Avoid resuming runtime-suspended
 lpss unnecessarily

Hi Lee,

On Thu, Sep 29, 2016 at 7:01 AM, Chen Yu <yu.c.chen@...el.com> wrote:
> We have report that the intel_lpss_prepare() takes too much time during
> suspend, and this is because we first resume the devices from runtime
> suspend by resume_lpss_device(), to make sure they are in proper state
> before system suspend, which takes 100ms for each LPSS devices(PCI power
> state from D3_cold to D0). And since resume_lpss_device() resumes the
> devices synchronously, we might get huge latency if we have many
> LPSS devices.
>
> So first try is to use pm_request_resume() instead, to make the runtime
> resume process asynchronously. Unfortunately the asynchronous runtime
> resume relies on pm_wq, which is freezed at early stage. So we choose
> another method, that is to avoid resuming runtime-suspended devices,
> if they are already runtime suspended. This is safe because for LPSS
> driver, the runtime suspend and system suspend are of the same
> hook - i.e., intel_lpss_suspend(). And moreover, this device is
> neither runtime wakeup source nor system wakeup source.
>
> Suggested-by: Rafael J. Wysocki <rafael.j.wysocki@...el.com>
> Acked-by: Mika Westerberg <mika.westerberg@...ux.intel.com>
> Reviewed-by: Andy Shevchenko <andriy.shevchenko@...ux.intel.com>
> Cc: Andy Shevchenko <andriy.shevchenko@...ux.intel.com>
> Cc: Mika Westerberg <mika.westerberg@...ux.intel.com>
> Cc: Rafael J. Wysocki <rafael.j.wysocki@...el.com>
> Cc: Lee Jones <lee.jones@...aro.org>
> Signed-off-by: Chen Yu <yu.c.chen@...el.com>

If this is fine with you and you'd like to apply it, please feel free
to add my ACK to it.

Alternatively, if you'd prefer me to apply it, please let me know.

> ---
>  drivers/mfd/intel-lpss.c | 9 +++++++++
>  include/linux/pm.h       | 7 +++++++
>  2 files changed, 16 insertions(+)
>
> diff --git a/drivers/mfd/intel-lpss.c b/drivers/mfd/intel-lpss.c
> index 41b1138..2583db8 100644
> --- a/drivers/mfd/intel-lpss.c
> +++ b/drivers/mfd/intel-lpss.c
> @@ -485,6 +485,15 @@ static int resume_lpss_device(struct device *dev, void *data)
>  int intel_lpss_prepare(struct device *dev)
>  {
>         /*
> +        * This is safe because:
> +        * 1. The runtime suspend and system suspend
> +        * are of the same hook.
> +        * 2. This device is neither runtime wakeup source
> +        * nor system wakeup source.
> +        */
> +       if (pm_runtime_status_suspended(dev))
> +               return DPM_DIRECT_COMPLETE;
> +       /*
>          * Resume both child devices before entering system sleep. This
>          * ensures that they are in proper state before they get suspended.
>          */
> diff --git a/include/linux/pm.h b/include/linux/pm.h
> index 06eb353..4a788b4 100644
> --- a/include/linux/pm.h
> +++ b/include/linux/pm.h
> @@ -786,4 +786,11 @@ enum dpm_order {
>         DPM_ORDER_DEV_LAST,
>  };
>
> +/*
> + * Return this from system suspend/hibernation ->prepare() callback to
> + * request the core to leave the device runtime-suspended during system
> + * suspend if possible.
> + */
> +#define DPM_DIRECT_COMPLETE 1
> +
>  #endif /* _LINUX_PM_H */
> --

Thanks,
Rafael