[PATCH v3 6/8] PM / ACPI: Enable the runtime PM centric approach for system sleep

[ulf.hansson@linaro.org (Ulf Hansson)]

On 2 September 2017 at 17:38, Rafael J. Wysocki <rjw@rjwysocki.net> wrote:
> On Friday, September 1, 2017 10:27:05 AM CEST Ulf Hansson wrote:
>> On 29 August 2017 at 17:27, Rafael J. Wysocki <rjw@rjwysocki.net> wrote:
>> > On Tuesday, August 29, 2017 4:56:48 PM CEST Ulf Hansson wrote:
>> >> This change enables the ACPI PM domain to cope with drivers that deploys
>> >> the runtime PM centric path for system sleep.
>> >
>> > [cut]
>> >
>> >> @@ -1052,11 +1066,20 @@ EXPORT_SYMBOL_GPL(acpi_subsys_complete);
>> >>   * @dev: Device to handle.
>> >>   *
>> >>   * Follow PCI and resume devices suspended at run time before running their
>> >> - * system suspend callbacks.
>> >> + * system suspend callbacks. However, try to avoid it in case the runtime PM
>> >> + * centric path is used for the device and then trust the driver to do the
>> >> + * right thing.
>> >>   */
>> >>  int acpi_subsys_suspend(struct device *dev)
>> >>  {
>> >> -     pm_runtime_resume(dev);
>> >> +     struct acpi_device *adev = ACPI_COMPANION(dev);
>> >> +
>> >> +     if (!adev)
>> >> +             return 0;
>> >> +
>> >> +     if (!dev_pm_is_rpm_sleep(dev) || acpi_dev_needs_resume(dev, adev))
>> >> +             pm_runtime_resume(dev);
>> >> +
>> >>       return pm_generic_suspend(dev);
>> >>  }
>> >>  EXPORT_SYMBOL_GPL(acpi_subsys_suspend);
>> >
>> > Well, I tried to avoid calling acpi_dev_needs_resume() for multiple times
>> > and that's why I added the update_state thing.
>> >
>> > Moreover, the is_rpm_sleep flag here has to mean not only that
>> > direct_complete should not be used with the device, but also that its driver
>> > is fine with not resuming it.
>>
>> Let me try to explain this better. I realize the changelog is
>> misleading around this particular section! Huh, apologize for that!
>>
>> First, patch1 makes the PM core treat the is_rpm_sleep flag as the
>> direct_complete isn't allowed for the device.
>>
>> For that reason, when the is_rpm_sleep is set, there is no point
>> calling acpi_dev_needs_resume() from acpi_subsys_prepare(), but
>> instead that can be deferred to acpi_subsys_suspend() - because it
>> doesn't matter if acpi_subsys_prepare() returns 0 or 1, in either case
>> the acpi_subsys_suspend() will be called. That's really what goes on
>> here.
>>
>> The end result is the same. If the acpi_dev_needs_resume() thinks that
>> the device needs to be runtime resumed, pm_runtime_resume() is called
>> for the device in acpi_subsys_suspend().
>>
>> So, this has nothing to do with whether the driver "is fine with not
>> resuming it" thing.
>
> No, sorry.
>
> If is_rpm_sleep was not set, the ACPI PM domain would resume the device in
> acpi_subsys_suspend() regardless of the acpi_dev_needs_resume() return value.

Yes, I believe I forgot about one scenario, when the direct_complete
path has been abandoned by the PM core, because a child device was
suspend before and it couldn't run the direct_complete path for it?

Just to be sure, that's the case you also had in mind?

> That's what's there in the patch.  So clearly, setting is_rpm_sleep means
> "this device does not need to be resumed in acpi_subsys_suspend() unless
> acpi_dev_needs_resume() returns true".  Which clearly means that the driver
> *is* fine with not resuming it, because if is_rpm_sleep is set, the device
> in fact may not be resumed and then the driver will need to cope with that.

Yes, I understand your concern, because we may break the default
behavior of the ACPI PM domain.

So, *if* there will be a next version, I will make sure to be better
safe than sorry, and add one flag per use case.

>
> And note that this meaning of is_rpm_sleep is different from what it is
> expected to mean to the core.
>
>> >
>> > IMO it is not a good idea to use one flag for these two different things at the
>> > same time at all.
>>
>> Yeah, I guess my upper comment addresses your immediate concern here?
>
> No, they don't.
>
>> However, there is one other thing the is_rpm_flag means. That is that
>> the driver has informed the ACPI PM domain, to trust the driver to
>> deal with system sleep, via re-using the runtime PM callbacks.
>> So the flag does still have two meanings, but that we can change - of course.
>
> I guess that you are referring to the use of dev_pm_is_rpm_sleep() in
> acpi_subsys_suspend_late()?  That's the third thing this flag means ...

Yes.

Kind regards
Uffe