[PATCH] PM / Domains: Power on the PM domain right after attach completes

[Dmitry Torokhov]

On Tue, Nov 18, 2014 at 12:28:26AM +0100, Rafael J. Wysocki wrote:
> On Monday, November 17, 2014 02:17:00 PM Dmitry Torokhov wrote:
> > On Mon, Nov 17, 2014 at 05:12:35PM -0500, Alan Stern wrote:
> > > On Mon, 17 Nov 2014, Dmitry Torokhov wrote:
> > > 
> > > > > >  Except buses
> > > > > > usually call pm_generic_runtime_resume() which ends up fetching driver's
> > > > > > callbacks. Maybe pm_generic_runtime_*() need be a bit smarter?
> > > > > 
> > > > > No, the bus subsystem needs to be smarter.  It shouldn't call 
> > > > > pm_generic_runtime_resume() if the driver hasn't been probed yet, or if 
> > > > > the driver has already been unbound from the device.
> > > > 
> > > > But that code wold be exactly the same for all buses, right? So why
> > > > can't pm_generic_runtime_resume() be smarter?
> > > 
> > > It would not be the same for all buses.  Each bus will have its own way 
> > > of recognizing whether or not a driver has been probed (i.e., by 
> > > checking some field in the bus-specific part of the device structure).
> > > 
> > > > However, is it allowed to call pm_runtime_get_sync() on devices that
> > > > didn't issue pm_runtime_enable()?
> > > 
> > > Yes.  But the bus has to issue pm_runtime_enable() before probing the 
> > > driver, because the driver will expect runtime PM to work properly 
> > > while its probe routine runs.  For example, the probe routine might 
> > > want to leave the device in a runtime-suspended state.  It can't do 
> > > that if the device isn't enabled for runtime PM.
> > 
> > That means that runtime PM will be enabled for all devices on given bus
> > while up till now drivers were deciding if their devices should be
> > runtime-pm-managed or not.
> 
> That's not the case for PCI drivers.
> 
> > I do not think we are quite ready for this.
> 
> We have to do that if power domains are in use, however, because if at least
> one device in a power domain in enabled for runtime PM, that will affect the
> other devices in that domain.
> 
> We could make a rule to keep a domail always up if at least one device in it
> has runtime PM disabled, but that is equivalent to enabling runtime PM for
> that device, powering the domain up and bumping up the device's usage counter.

What will driver will see if it tries to check pm_runtime_active()?
Would not it get unexpected result if the driver did not call
pm_runtime_enable() on it's device?

-- 
Dmitry