Re: [PATCH 1/1] PM / Runtime: let rpm_resume fail if rpm disabled and device suspended.

["Rafael J. Wysocki" <rjw@rjwysocki.net>]

On Tuesday, June 17, 2014 10:26:14 PM Rafael J. Wysocki wrote:
> On Tuesday, June 17, 2014 10:11:32 AM Alan Stern wrote:
> > On Mon, 16 Jun 2014, Rafael J. Wysocki wrote:
> > 
> > > > For reasons having nothing to do with Allen's suggested change, I
> > > > wonder if we shouldn't replace this line with something like:
> > > > 
> > > > -	else if (dev->power.disable_depth == 1 && dev->power.is_suspended
> > > > +	else if (dev->power.disable > 0 && !dev->power.is_suspended
> > > > 	    && dev->power.runtime_status == RPM_ACTIVE)
> > > > 		retval = 1;
> > > > 
> > > > It seems that I've been bitten by this several times in the past.  
> > > > When a device is disabled for runtime PM, and more or less permanently
> > > > stuck in the RPM_ACTIVE state, calls to pm_runtime_resume() or
> > > > pm_runtime_get_sync() shouldn't fail.
> > > > 
> > > > For example, suppose some devices of a certain type support runtime 
> > > > power management but others don't.  We naturally want to call 
> > > > pm_runtime_disable() for the ones that don't.  But we also want the 
> > > > same driver to work for all the devices, which means that 
> > > > pm_runtime_get_sync() should return success -- otherwise the driver 
> > > > will think that something has gone wrong.
> > > > 
> > > > Rafael, what do you think?
> > > 
> > > That condition is there specifically to take care of the system suspend
> > > code path.  It means that if runtime PM is disabled, but it only has been
> > > disabled by the system suspend code path, we should treat the device as
> > > "active" (ie. return 1).  That won't work after the proposed change.
> > 
> > Ah, yes, quite true.  Okay, suppose we replace that line with just:
> > 
> > +	else if (dev->power.disable > 0
> > 
> > > I guess drivers that want to work with devices where runtime PM may be
> > > disabled can just check the return value of rpm_resume() for -EACCES?
> > 
> > They could, but it's extra work and it's extremely easy to forget 
> > about.  I'd prefer not to do things that way.
> 
> In that case we need to audit all code that checks the return value of
> __pm_runtime_resume() to verify that it doesn't depend on the current
> behavior in any way.  It shouldn't, but still.
> 
> Also we probably should drop the -EACCES return value from rpm_resume() in the
> same patch, because it specifically only covers the dev->power.disable > 0 case
> (which BTW is consistent with the suspend side of things, so I'm totally unsure
> about that being the right thing to do to be honest).

Perhaps it'd be better to rework __pm_runtime_resume() to convert the -EACCES
return value from rpm_resume() into 0 if RPM_GET_PUT is set?

Rafael