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

Alan Stern
2014-06-19T14:34:05Z

On Thu, 19 Jun 2014, Rafael J. Wysocki wrote:

> Well, we used to have the notion that runtime_status is not meaningful for
> devices with dev->power.disable_depth greater than 0 (except for the special
> case in the suspend code path where we know why it is greater than 0). I think
> it was useful. :-)

Did we really have that notion? My memory is a little cloudy, but I
thought we decided that runtime_status would not be meaningful when
dev->power.runtime_error was set -- not when dev->power.disable_depth
was greater than 0. Am I mixed up?

In any case, I think it is reasonable to regard runtime_status as
meaningful when disable_depth > 0. The PM core isn't allowed to invoke
the runtime callbacks at such times, that's all. This makes perfect
sense for a device that doesn't support power management and hence must
always be at full power. Or when a driver knows that runtime_status is
out of agreement with the device's actual power state and wants to
update runtime_status directly.

> > So pm_runtime_resume() and pm_request_resume() would still fail, but
> > pm_runtime_get() and pm_runtime_get_sync() would work? I'm not sure
> > about the reason for this distinction.
>
> The meaning of pm_runtime_get()/pm_runtime_get_sync() is "prevent the
> device from being suspended from now on and resume it if necessary" while
> "runtime PM disabled and runtime_status == RPM_ACTIVE" may be interpreted
> as "not necessary to resume", so it is reasonable to special case this
> particular situation for these particular routines IMHO.

By the same reasoning, the meaning of pm_runtime_resume() is "resume
the device now if necsesary". Since "runtime PM disabled and
runtime_status == RPM_ACTIVE" means "not necessary to resume", isn't it
logical for pm_runtime_resume() also to succeed under that condition?

Alan Stern