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

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Date:	Thu, 19 Jun 2014 10:34:01 -0400 (EDT)
From:	Alan Stern <stern@...land.harvard.edu>
To:	"Rafael J. Wysocki" <rjw@...ysocki.net>
cc:	Allen Yu <alleny@...dia.com>, Pavel Machek <pavel@....cz>,
	Len Brown <len.brown@...el.com>,
	Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
	<linux-pm@...r.kernel.org>, <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH 1/1] PM / Runtime: let rpm_resume fail if rpm disabled
 and device suspended.

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

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