linux-kernel - Re: [linux-pm] calling runtime PM from system PM methods

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Date:	Sat, 18 Jun 2011 21:42:04 -0400 (EDT)
From:	Alan Stern <stern@...land.harvard.edu>
To:	"Rafael J. Wysocki" <rjw@...k.pl>
cc:	linux-pm@...ts.linux-foundation.org, <linux-omap@...r.kernel.org>,
	Kevin Hilman <khilman@...com>, Paul Walmsley <paul@...an.com>,
	Magnus Damm <magnus.damm@...il.com>,
	LKML <linux-kernel@...r.kernel.org>
Subject: Re: [linux-pm] calling runtime PM from system PM methods

On Sun, 19 Jun 2011, Rafael J. Wysocki wrote:

> On Saturday, June 18, 2011, Rafael J. Wysocki wrote:
> > On Saturday, June 18, 2011, Alan Stern wrote:
> > > On Sat, 18 Jun 2011, Rafael J. Wysocki wrote:
> ...
> > 
> > Well, assuming that https://patchwork.kernel.org/patch/893722/ is applied,
> > which is going to be, I think we can put
> > 
> > +       pm_runtime_get_noresume(dev);
> > +       pm_runtime_enable(dev);
> > 
> > in device_resume() after the dev->power.is_suspended check and
> > pm_runtime_put_noidle() under the End label.  That cause them to
> > be called under the device lock, but that shouldn't be a big deal.
> > 
> > Accordingly, we can call pm_runtime_disable(dev) in __device_suspend(),
> > right next to the setting of power.is_suspended.
> > 
> > This is implemented by the patch below.
> 
> Well, it hangs suspend on my Toshiba test box, I'm not sure why exactly.
> 
> This happens even if the pm_runtime_disable() is replaced with a version
> that only increments the disable depth, so it looks like something down
> the road relies on disable_depth being zero.  Which is worrisome.

This is a sign that the PM subsystem is getting a little too 
complicated.  :-(

> Trying to figure out what the problem is I noticed that, for example,
> the generic PM operations use pm_runtime_suspended() to decide whether or
> not to execute system suspend callbacks, so the patch below would break it.
> 
> Also, after commit e8665002477f0278f84f898145b1f141ba26ee26 the
> pm_runtime_suspended() check in __pm_generic_call() doesn't really make
> sense.

In light of the recent changes, we should revisit the decisions behind 
the generic PM operations.

Alan Stern

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