linux-kernel - Re: [PATCH][v2] mfd: intel-lpss: Avoid resuming runtime-suspended lpss unnecessarily

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Date:   Wed, 28 Sep 2016 23:48:40 +0200
From:   "Rafael J. Wysocki" <rafael@...nel.org>
To:     Chen Yu <yu.c.chen@...el.com>
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>,
        Lee Jones <lee.jones@...aro.org>
Subject: Re: [PATCH][v2] mfd: intel-lpss: Avoid resuming runtime-suspended
 lpss unnecessarily

On Wed, Sep 28, 2016 at 6:29 PM, 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>
> ---
>  drivers/mfd/intel-lpss.c | 9 +++++++++
>  include/linux/pm.h       | 3 +++
>  2 files changed, 12 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..5606ad9 100644
> --- a/include/linux/pm.h
> +++ b/include/linux/pm.h
> @@ -786,4 +786,7 @@ enum dpm_order {
>         DPM_ORDER_DEV_LAST,
>  };
>
> +/* The device is OK to remain runtime-suspended during suspend.*/

/*
 * 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 */
> --

But it is fine by me overall.

Thanks,
Rafael