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

Alan Stern
2014-06-17T14:11:34Z

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.

Alan Stern