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

[Chen Yu <yu.c.chen@intel.com>]

On Wed, Sep 28, 2016 at 11:48:40PM +0200, Rafael J. Wysocki wrote:
> On Wed, Sep 28, 2016 at 6:29 PM, Chen Yu <yu.c.chen@intel.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@intel.com>
> > Acked-by: Mika Westerberg <mika.westerberg@linux.intel.com>
> > Reviewed-by: Andy Shevchenko <andriy.shevchenko@linux.intel.com>
> > Cc: Andy Shevchenko <andriy.shevchenko@linux.intel.com>
> > Cc: Mika Westerberg <mika.westerberg@linux.intel.com>
> > Cc: Rafael J. Wysocki <rafael.j.wysocki@intel.com>
> > Cc: Lee Jones <lee.jones@linaro.org>
> > Signed-off-by: Chen Yu <yu.c.chen@intel.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.
>  */
>
I've taken this comment in a new version, thanks! 
> > +#define DPM_DIRECT_COMPLETE 1
> > +
> >  #endif /* _LINUX_PM_H */
> > --
> 
> But it is fine by me overall.
> 
> Thanks,
> Rafael