Re: [PATCH] OMAPDSS: Check if RPM enabled before trying to change state

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On Tue, 26 Jun 2012, Grazvydas Ignotas wrote:

> CCing some PM people, maybe they can comment?
> 
> On Tue, Jun 26, 2012 at 7:51 AM, Rajendra Nayak <rnayak@xxxxxx> wrote:
> > On Monday 25 June 2012 06:20 PM, Tomi Valkeinen wrote:
> >>
> >> Do you know how the drivers should handle CONFIG_PM_RUNTIME=n?
> >> Are they supposed to handle the error values returned by runtime PM
> >> functions somehow, or should they use #ifdef CONFIG_PM_RUNTIME?
> >
> > hmm, I always though with CONFIG_RUNTIME_PM=n, the functions would
> > be stubbed to return success and not failure.

Not exactly.  They are stubbed to indicate that the device cannot be 
suspended, that it is always active.

Failure to suspend a device should not be regarded as particularly bad, 
because it doesn't affect the device's functionality.  That's true even 
when CONFIG_RUNTIME_PM is enabled.

> And the _pm_runtime_resume
> > function indeed seems to return 1, which is not failure but just saying
> > that your device is already active/enabled.
> > The _pm_runtime_suspend and _pm_runtime_idle do return a -ENOSYS, which
> > is something only returned when CONFIG_RUNTIME_PM=n, so if you really
> > want to handle failing pm_runtime_put_sync cases, maybe you still can.
> > But then, I don't know if there is anything you can do to recover from
> > a failing pm_runtime_put_sync, except for warning the user maybe.

I don't see much point in warning the user that a device was unable to 
go to low power.

Alan Stern

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