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

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Date:	Wed, 11 May 2011 21:11:50 +0200
From:	"Rafael J. Wysocki" <rjw@...k.pl>
To:	Jonathan Corbet <corbet@....net>
Cc:	Linux PM mailing list <linux-pm@...ts.linux-foundation.org>,
	Greg KH <gregkh@...e.de>, LKML <linux-kernel@...r.kernel.org>,
	Kevin Hilman <khilman@...com>,
	Grant Likely <grant.likely@...retlab.ca>,
	Magnus Damm <magnus.damm@...il.com>, linux-sh@...r.kernel.org,
	MyungJoo Ham <myungjoo.ham@...il.com>,
	Guennadi Liakhovetski <g.liakhovetski@....de>
Subject: Re: [PATCH 3/5] PM: Support for system-wide power transitions in generic power domains

On Wednesday, May 11, 2011, Jonathan Corbet wrote:
> Hi, Rafael,
> 
> One small question that came to mind as I was looking at this patch:
> 
> > +/**
> > + * 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;
> 
> I'm not quite sure why this function exists?  The lock doesn't really
> change anything, since the power state can change before or after this
> check regardless.  If you need the power state to be stable, it seems like
> the lock needs to be taken further up the stack; otherwise simply checking
> genpd->power_is_off directly would seem to be sufficient. Am I missing
> something?

No, you aren't. :-)

In fact, the function doesn't exist any more in the most recent version
of the patch: https://patchwork.kernel.org/patch/775412/

Thanks,
Rafael
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