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

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Date:	Fri, 07 Nov 2014 09:06:41 +0100
From:	Krzysztof Kozlowski <k.kozlowski@...sung.com>
To:	"Rafael J. Wysocki" <rjw@...ysocki.net>
Cc:	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>,
	Alan Stern <stern@...land.harvard.edu>,
	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 czw, 2014-11-06 at 23:51 +0100, Rafael J. Wysocki wrote:
> On Thursday, November 06, 2014 09:36:46 AM Krzysztof Kozlowski wrote:
> > Some drivers (e.g. bus drivers) may want to check if power.irq_safe was
> > called by child driver, regardless of CONFIG_PM_RUNTIME.
> > 
> > An example scenario is amba/bus.c and dma/pl330.c drivers. The runtime
> > suspend/resume callbacks in amba bus driver act differently if irq_safe
> > was set by child driver (in irq_safe mode bus clock is only disabled).
> > 
> > The pl330 driver sets irq_safe and assumes that amba bus driver will
> > only disable the clock in runtime PM. So in system sleep suspend
> > callback the pl330 driver unprepares the clock after calling
> > pm_runtime_force_suspend().
> > 
> > However inconsistency would appear if CONFIG_PM_RUNTIME is not set and
> > child drivers do not want the irq_safe runtime PM. In such case amba bus
> > driver still has to know whether child driver wanted irq_safe - by
> > looking at dev->power.irq_safe field.
> > 
> > Signed-off-by: Krzysztof Kozlowski <k.kozlowski@...sung.com>
> > ---
> >  include/linux/pm.h         | 2 +-
> >  include/linux/pm_runtime.h | 5 ++++-
> >  2 files changed, 5 insertions(+), 2 deletions(-)
> > 
> > diff --git a/include/linux/pm.h b/include/linux/pm.h
> > index 383fd68aaee1..b05fa954f50d 100644
> > --- a/include/linux/pm.h
> > +++ b/include/linux/pm.h
> > @@ -566,6 +566,7 @@ struct dev_pm_info {
> >  	bool			ignore_children:1;
> >  	bool			early_init:1;	/* Owned by the PM core */
> >  	bool			direct_complete:1;	/* Owned by the PM core */
> > +	unsigned int		irq_safe:1;	/* PM runtime */
> >  	spinlock_t		lock;
> >  #ifdef CONFIG_PM_SLEEP
> >  	struct list_head	entry;
> > @@ -590,7 +591,6 @@ struct dev_pm_info {
> >  	unsigned int		run_wake:1;
> >  	unsigned int		runtime_auto:1;
> >  	unsigned int		no_callbacks:1;
> > -	unsigned int		irq_safe:1;
> >  	unsigned int		use_autosuspend:1;
> >  	unsigned int		timer_autosuspends:1;
> >  	unsigned int		memalloc_noio:1;
> 
> 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.

Best regards,
Krzysztof


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