linux-kernel - Re: [PATCH] PM / Runtime: honor device autosuspend in pm_generic_runtime

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Date:	Tue, 28 May 2013 22:59:07 +0200
From:	"Rafael J. Wysocki" <rjw@...k.pl>
To:	Alan Stern <stern@...land.harvard.edu>
Cc:	Mika Westerberg <mika.westerberg@...ux.intel.com>,
	linux-pm@...r.kernel.org, Pavel Machek <pavel@....cz>,
	"Rafael J. Wysocki" <rafael.j.wysocki@...el.com>,
	Len Brown <len.brown@...el.com>,
	Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH] PM / Runtime: honor device autosuspend in pm_generic_runtime_idle()

On Tuesday, May 28, 2013 10:13:35 AM Alan Stern wrote:
> On Tue, 28 May 2013, Rafael J. Wysocki wrote:
> 
> > On Monday, May 13, 2013 01:50:18 PM Rafael J. Wysocki wrote:
> > > On Monday, May 13, 2013 02:05:27 PM Mika Westerberg wrote:
> > > > If the device is using autosuspend we should honor that and call
> > > > pm_runtime_autosuspend() instead of pm_runtime_suspend(). Failing to do so
> > > > causes the device to be suspended immediately even though it expects to be
> > > > suspended only when the autosuspend delay is expired.
> > > > 
> > > > Signed-off-by: Mika Westerberg <mika.westerberg@...ux.intel.com>
> > > > ---
> > > >  drivers/base/power/generic_ops.c |    5 ++++-
> > > >  1 file changed, 4 insertions(+), 1 deletion(-)
> > > > 
> > > > diff --git a/drivers/base/power/generic_ops.c b/drivers/base/power/generic_ops.c
> > > > index bfd898b..19786ca 100644
> > > > --- a/drivers/base/power/generic_ops.c
> > > > +++ b/drivers/base/power/generic_ops.c
> > > > @@ -29,7 +29,10 @@ int pm_generic_runtime_idle(struct device *dev)
> > > >  			return ret;
> > > >  	}
> > > >  
> > > > -	pm_runtime_suspend(dev);
> > > > +	if (dev->power.use_autosuspend)
> > > > +		pm_runtime_autosuspend(dev);
> > > > +	else
> > > > +		pm_runtime_suspend(dev);
> > > >  	return 0;
> > > 
> > > First of all, this is racy (power.use_autosuspend shoud be accessed under
> > > power.lock).
> > > 
> > > Second, this is not the only place we'd need to make this change (the analogous
> > > function for PCI is one example, but there may be others).
> > > 
> > > Finally, I'm not sure how to address this problem in general.  It may be better
> > > to simply modify rpm_idle() and remove pm_generic_runtime_idle() etc. entirely.
> > > 
> > > I'll have a look at that, thanks for pointing out the problem.
> > 
> > I'm not sure if the core is the right place to address this, because it's
> > not entirely clear if all drivers using autosuspend will have the same policy
> > with respect to pm_runtime_idle() (i.e. to avoid suspending immediately if
> > the suspend delay timer is active).
> > 
> > In my opinion it'd be better to address that in the driver by adding a
> > .runtime_idle() callback executing pm_runtime_autosuspend(dev) and returning
> > -EBUSY.
> 
> Remember that the return value from the runtime_idle callback is ignored.

It is ignored by the core, but some subsystems (those using
pm_generic_runtime_idle() in particular) take it into account.

> Are you suggesting that the PM core should start paying attention to it?

In fact, I was pondering posting a patch making that change. :-)

Perhaps I'll just post it for discussion later today ...

Thanks,
Rafael


-- 
I speak only for myself.
Rafael J. Wysocki, Intel Open Source Technology Center.
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