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

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Date:   Tue, 4 Oct 2016 15:55:28 +0100
From:   Lee Jones <lee.jones@...aro.org>
To:     "Rafael J. Wysocki" <rafael@...nel.org>
Cc:     Chen Yu <yu.c.chen@...el.com>, 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

On Fri, 30 Sep 2016, Rafael J. Wysocki wrote:

> On Fri, Sep 30, 2016 at 2:29 AM, Lee Jones <lee.jones@...aro.org> wrote:
> > On Fri, 30 Sep 2016, Rafael J. Wysocki wrote:
> >
> >> 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.
> >
> > You want this in for v3.9?
> 
> I'd rather queue it up for 4.10 (assuming that the above and below
> major version numbers are simply off by one by mistake).

Yes, of course they are off by one.

This is what happens when you conduct mail duties with jetlag. :)

> > I just started applying patches for v3.10.
> >
> > If you're certain there are 0% chance of regressions, I will still
> > apply this for v3.9 with your Ack.
> 
> 4.10 should be fine.

Great.

> >> > ---
> >> >  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

-- 
Lee Jones
Linaro STMicroelectronics Landing Team Lead
Linaro.org │ Open source software for ARM SoCs
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