linux-kernel - Re: [PATCH v10 1/5] PM / Runtime: Allow accessing irq_safe if no PM

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Date:	Sat, 08 Nov 2014 00:45:52 +0100
From:	"Rafael J. Wysocki" <rjw@...ysocki.net>
To:	Alan Stern <stern@...land.harvard.edu>
Cc:	Krzysztof Kozlowski <k.kozlowski@...sung.com>,
	Len Brown <len.brown@...el.com>, Pavel Machek <pavel@....cz>,
	Russell King <linux@....linux.org.uk>,
	Dan Williams <dan.j.williams@...el.com>,
	Vinod Koul <vinod.koul@...el.com>,
	Ulf Hansson <ulf.hansson@...aro.org>, linux-pm@...r.kernel.org,
	linux-kernel@...r.kernel.org, dmaengine@...r.kernel.org,
	Lars-Peter Clausen <lars@...afoo.de>,
	Michal Simek <michal.simek@...inx.com>,
	Kevin Hilman <khilman@...nel.org>,
	Laurent Pinchart <laurent.pinchart@...asonboard.com>,
	Kyungmin Park <kyungmin.park@...sung.com>,
	Marek Szyprowski <m.szyprowski@...sung.com>,
	Bartlomiej Zolnierkiewicz <b.zolnierkie@...sung.com>
Subject: Re: [PATCH v10 1/5] PM / Runtime: Allow accessing irq_safe if no PM_RUNTIME

On Friday, November 07, 2014 09:50:58 AM Alan Stern wrote:
> On Fri, 7 Nov 2014, Krzysztof Kozlowski wrote:
> 
> > > Well, that is a good reason to introduce a wrapper around power.irq_safe in my
> > > view.
> > > 
> > > And define the wrapper so that it always returns false for CONFIG_PM_RUNTIME
> > > unset.
> > > 
> > > This way not only you wouldn't need to move the flag from under the #ifdef,
> > > but also you would make the compiler skip the relevant pieces of code
> > > entiretly for CONFIG_PM_RUNTIME unset.
> > 
> > Few days ago I would be happy with your opinion :), but know I think
> > this is better solution than wrapper. Consider case:
> > 1. PM_RUNTIME unset.
> > 2. System suspends.
> > 3. The pl330 in its suspend callback calls force_runtime_suspend which
> > leads us to amba/bus.
> > 4. The amba/bus.c in runtime suspend checks for irq_safe (it is FALSE),
> > so it disables and unprepares the clock.
> > 5. The pl330 in probe requested irq_safe so it assumes amba/bus will
> > only disable the clock. So the pl330 unprepares the clock. Again.
> 
> To me, this sounds like a good reason to avoid using 
> force_runtime_suspend().  In fact, it sounds like a good reason to 
> avoid relying on the runtime PM mechanism to handle non-runtime-PM 
> things (like a system suspend callback).  If CONFIG_PM_RUNTIME isn't 
> enabled then the runtime PM stack simply should not be used.

Amen.

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