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

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Date:	Mon, 10 Nov 2014 11:36:10 -0500 (EST)
From:	Alan Stern <stern@...land.harvard.edu>
To:	Ulf Hansson <ulf.hansson@...aro.org>
cc:	Krzysztof Kozlowski <k.kozlowski@...sung.com>,
	"Rafael J. Wysocki" <rjw@...ysocki.net>,
	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>,
	"linux-pm@...r.kernel.org" <linux-pm@...r.kernel.org>,
	"linux-kernel@...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 Mon, 10 Nov 2014, Ulf Hansson wrote:

> > 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.
> 
> There are an important advantage of using the pm_runtime_force_suspend() here.
> 
> For the driver to handle clock gating at system PM suspend, it first
> needs to bring the device into full power, through
> pm_runtime_get_sync(). Otherwise it's not safe to gate the clock,
> since it may already be gated.

That's fine, but it has nothing to do with pm_runtime_force_suspend().

Besides, if the real question is whether or not to gate the clock (or 
in other words, has the clock already been gated), why not just store a 
"clock_is_gated" flag somewhere?

Alan Stern

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