[PATCH v2 5/9] PM / ACPI: Provide option to disable direct_complete for ACPI devices

[Rafael J. Wysocki]

On Thursday, August 24, 2017 2:13:55 AM CEST Rafael J. Wysocki wrote:
> On Thursday, August 24, 2017 1:39:44 AM CEST Rafael J. Wysocki wrote:
> > On Wed, Aug 23, 2017 at 4:42 PM, Ulf Hansson <ulf.hansson at linaro.org> wrote:
> > > In some cases a driver for an ACPI device needs to be able to prevent the
> > > ACPI PM domain from using the direct_complete path during system sleep.
> > >
> > > One typical case is when the driver for the device needs its device to stay
> > > runtime enabled, during the __device_suspend phase. This isn't the case
> > > when the direct_complete path is being executed by the PM core, as it then
> > > disables runtime PM for the device in __device_suspend(). Any following
> > > attempts to runtime resume the device after that point, just fails.
> > 
> > OK, that is a problem.
> > 
> > > A workaround to this problem is to let the driver runtime resume its device
> > > from its ->prepare() callback, as that would prevent the direct_complete
> > > path from being executed. However, that may often be a waste, especially if
> > > it turned out that no one really needed the device.
> > >
> > > For this reason, invent acpi_dev_disable|enable_direct_complete(), to allow
> > > drivers to inform the ACPI PM domain to change its default behaviour during
> > > system sleep, and thus control whether it may use the direct_complete path
> > > or not.
> > 
> > But I'm not sure this is the right place to address it as it very well
> > may affect a PCI device too.
> > 
> > Also, this is about the device and not about its ACPI companion
> > object, so putting the flag in there is somewhat unclean, so to speak.
> > 
> > It looks like we need a flag in dev_pm_info saying something along the
> > lines of "my system suspend callback can deal with runtime PM" that
> > will cause the direct_complete update to occur in
> > __device_suspend_late() instead of __device_suspend().
> 
> IOW, something like the patch below.
> 
> It actually should work with the ACPI PM domain code as is except that it
> will cause the device to be runtime resumed every time during suspend.
> 
> But acpi_subsys_suspend() can be changed to avoid resuming the device if
> power.force_suspend is set.

Or better yet, if power.direct_complete is not set, because that means the
device needs to be resumed anyway.

And if power.direct_complete is set at that point, power.force_suspend has to
be set too.