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

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 [off-list ref] wrote:

quoted

On Monday 25 June 2012 06:20 PM, Tomi Valkeinen wrote:

quoted

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

quoted

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