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

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Message-ID: <20161216231942.GA12460@wunner.de>
Date:   Sat, 17 Dec 2016 00:19:42 +0100
From:   Lukas Wunner <lukas@...ner.de>
To:     Lee Jones <lee.jones@...aro.org>
Cc:     linux-pm@...r.kernel.org, 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>,
        Chen Yu <yu.c.chen@...el.com>
Subject: Re: [PATCH v3] mfd: intel-lpss: Avoid resuming runtime-suspended
 lpss unnecessarily

Hi Lee,

you wrote on Oct 4 that you applied the below patch for v4.10.
However I don't see the patch on your for-mfd-next branch.
Maybe the patch slipped between the cracks, please double-check.
I would like to use the DPM_DIRECT_COMPLETE macro introduced by it
in a patch of my own.

I also don't see a pull from you in Linus' tree yet. Please note
that this merge window will be shorter than usual and pulls should
be sent out before coming Friday.

Thanks,

Lukas

On Thu, Sep 29, 2016 at 01:01:26PM +0800, Chen Yu 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       | 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 */