Messages in this thread | | | Subject | Re: [PATCH][RFC] mfd: intel-lpss: Avoid resuming runtime-suspended lpss unnecessarily | From | "Rafael J. Wysocki" <> | Date | Tue, 13 Sep 2016 14:15:36 +0200 |
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On 9/13/2016 10:24 AM, Lee Jones wrote: > On Mon, 12 Sep 2016, Chen Yu wrote: >> On Mon, Sep 12, 2016 at 04:17:04PM +0100, Lee Jones wrote: >>> On Sun, 04 Sep 2016, 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. >>>> >>>> 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> >>>> Signed-off-by: Chen Yu <yu.c.chen@intel.com> >>>> --- >>>> drivers/mfd/intel-lpss.c | 9 +++++++++ >>>> 1 file changed, 9 insertions(+) >>>> >>>> diff --git a/drivers/mfd/intel-lpss.c b/drivers/mfd/intel-lpss.c >>>> index 41b1138..6dcc9a0 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 1; >>> What's '1'? >>> >> According to the comment in device_prepare(): >> >> A positive return value from ->prepare() means "this device appears >> to be runtime-suspended and its state is fine, so if it really is >> runtime-suspended, you can leave it in that state provided that you >> will do the same thing with all of its descendants". > Are there no defines for this? >
Not at the moment, but I guess they can be added if really necessary. :-)
But that said it doesn't have to be 1 or any specific value. Any positive number will have the same effect.
Thanks,
Rafael
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