Re: [linux-pm] pm_runtime_suspended() and non-pm_runtime-using (i2c) drivers

["Rafael J. Wysocki" <rjw-KKrjLPT3xs0@public.gmane.org>]

On Tuesday, December 14, 2010, Alan Stern wrote:
> On Tue, 14 Dec 2010, Rabin Vincent wrote:
> 
> > Hello,
> > 
> > If an i2c driver uses dev_pm_ops and pm_runtime_suspended() returns true
> > for the device,  the i2c core will not call the driver's pm->suspend()
> > routine.  Similar behaviour (except for the if dev_pm_ops check) is
> > present in the generic PM ops provided in
> > drivers/base/power/generic_ops.c.
> > 
> > Since pm_runtime_suspended() returns true if the relevant driver did not
> > call any pm_runtime functions, this means that any driver which does not
> > use pm_runtime APIs will not get its pm->suspend() callback called
> > during system sleep, if CONFIG_PM_RUNTIME is enabled.
> > 
> > For the i2c case, there are several such drivers (in drivers/input/*,
> > etc) lacking these calls.  How is this to be handled?  Do all of these
> > drivers need to be patched to use the pm_runtime API if they are to be
> > used on a kernel with PM_RUNTIME enabled?
> 
> I'm not familiar with the details of how the i2c subsystem works.  But
> in general, the subsystem code should call pm_runtime_set_active()  
> for every device before registering it.  Then if a driver doesn't use
> any runtime-PM functions, pm_runtime_suspended() will return false.

I rather think that our current definition of pm_runtime_suspended() is
not really adequate.

Namely, it shouldn't really return true if runtime PM is not enabled
(ie. power.disable_depth > 1).  That change would fix the issue at hand,
wouldn't it?

Rafael