linux-kernel - Re: [linux-pm] [PATCH 3/5] PM: Support for system-wide power transitions in generic power domains

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Message-Id: <201105092120.42005.rjw@sisk.pl>
Date:	Mon, 9 May 2011 21:20:41 +0200
From:	"Rafael J. Wysocki" <rjw@...k.pl>
To:	Alan Stern <stern@...land.harvard.edu>
Cc:	Linux PM mailing list <linux-pm@...ts.linux-foundation.org>,
	linux-sh@...r.kernel.org, Greg KH <gregkh@...e.de>,
	LKML <linux-kernel@...r.kernel.org>,
	Grant Likely <grant.likely@...retlab.ca>,
	Guennadi Liakhovetski <g.liakhovetski@....de>
Subject: Re: [linux-pm] [PATCH 3/5] PM: Support for system-wide power transitions in generic power domains

On Monday, May 09, 2011, Alan Stern wrote:
> On Sun, 8 May 2011, Rafael J. Wysocki wrote:
> 
> > From: Rafael J. Wysocki <rjw@...k.pl>
> > 
> > Make generic power domains support system-wide power transitions
> > (system suspend and hibernation).  Add suspend, resume, freeze and
> > thaw callbacks to be associated with struct generic_power_domain
> > objects and make pm_genpd_init() use them as appropriate.
> 
> ...
> 
> > Index: linux-2.6/drivers/base/power/domain.c
> > ===================================================================
> > --- linux-2.6.orig/drivers/base/power/domain.c
> > +++ linux-2.6/drivers/base/power/domain.c
> > @@ -273,6 +273,280 @@ static int pm_genpd_runtime_resume(struc
> >  
> >  #endif /* CONFIG_PM_RUNTIME */
> >  
> > +#ifdef CONFIG_PM_SLEEP
> > +
> > +/**
> > + * pm_genpd_powered_down - Check if power has been removed from a power domain.
> > + * @genpd: Power domain to check.
> > + */
> > +static bool pm_genpd_powered_down(struct generic_power_domain *genpd)
> > +{
> > +	bool ret;
> > +
> > +	mutex_lock(&genpd->lock);
> > +	ret = genpd->power_is_off;
> > +	mutex_unlock(&genpd->lock);
> > +
> > +	return ret;
> > +}
> 
> What is the purpose of the mutex?  On the face of it, there's nothing 
> to prevent another thread from changing the domain's power state in 
> between the mutex_unlock() call and the return statement.

Now, that I think of it, the mutex isn't really necessary.

genpd->power_is_off is only changed by the runtime PM code that will
never be called during system suspend if genpd->power_is_off is set
already.

I'm going to post an update shortly, I'll include a fix for that in it.

Thanks,
Rafael
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