Re: [PATCH v8 1/5] PM / Runtime: Add getter for querying the IRQ safe option

From: Krzysztof Kozlowski <k.kozlowski@samsung.com>
To: Pavel Machek <pavel@ucw.cz>
Cc: "Rafael J. Wysocki" <rjw@rjwysocki.net>,
	Len Brown <len.brown@intel.com>, Jonathan Corbet <corbet@lwn.net>,
	Russell King <linux@arm.linux.org.uk>,
	Dan Williams <dan.j.williams@intel.com>,
	Vinod Koul <vinod.koul@intel.com>,
	Ulf Hansson <ulf.hansson@linaro.org>,
	Alan Stern <stern@rowland.harvard.edu>,
	linux-pm@vger.kernel.org, linux-doc@vger.kernel.org,
	linux-kernel@vger.kernel.org, dmaengine@vger.kernel.org,
	Lars-Peter Clausen <lars@metafoo.de>,
	Michal Simek <michal.simek@xilinx.com>,
	Kyungmin Park <kyungmin.park@samsung.com>,
	Marek Szyprowski <m.szyprowski@samsung.com>,
	Bartlomiej Zolnierkiewicz <b.zolnierkie@samsung.com>
Subject: Re: [PATCH v8 1/5] PM / Runtime: Add getter for querying the IRQ safe option
Date: Fri, 31 Oct 2014 15:40:16 +0100	[thread overview]
Message-ID: <1414766416.6537.6.camel@AMDC1943> (raw)
In-Reply-To: <20141031142241.GA17547@amd>

On pią, 2014-10-31 at 15:22 +0100, Pavel Machek wrote:
> On Fri 2014-10-31 10:14:55, Krzysztof Kozlowski wrote:
> > On pon, 2014-10-20 at 11:04 +0200, Krzysztof Kozlowski wrote:
> > > Add a simple getter pm_runtime_is_irq_safe() for querying whether runtime
> > > PM IRQ safe was set or not.
> > > 
> > > Various bus drivers implementing runtime PM may use choose to suspend
> > > differently based on IRQ safeness status of child driver (e.g. do not
> > > unprepare the clock if IRQ safe is not set).
> > > 
> > > Signed-off-by: Krzysztof Kozlowski <k.kozlowski@samsung.com>
> > > Reviewed-by: Ulf Hansson <ulf.hansson@linaro.org>
> > 
> > Rafael, Len, Pavel,
> > 
> > Is proposed API ok? Do you have any comments?
> > 
> > I'll upload whole patchset to Russell's patch tracking system. However
> > an ack from PM maintainer is probably needed.
> 
> I don't like the API. Having callbacks work in different context (irq
> / noirq) based on what another function reports is ugly.
> 
> What is the penalty if we always decide callbacks are not IRQ safe?

Then pm_runtime_get_sync() could not be called in atomic context. The
pl330 runtime PM would have to be completely reworked because one
pm_runtime_get_sync() is called in device_issue_pending which cannot
sleep (at least in non preemptible kernels). Probably this can be solved
some way... 

Best regards,
Krzysztof

> 
> > > --- a/Documentation/power/runtime_pm.txt
> > > +++ b/Documentation/power/runtime_pm.txt
> > > @@ -468,6 +468,10 @@ drivers/base/power/runtime.c and include/linux/pm_runtime.h:
> > >      - set the power.irq_safe flag for the device, causing the runtime-PM
> > >        callbacks to be invoked with interrupts off
> > >  
> > > +  bool pm_runtime_is_irq_safe(struct device *dev);
> > > +    - return true if power.irq_safe flag was set for the device, causing
> > > +      the runtime-PM callbacks to be invoked with interrupts off
> > > +
> > >    void pm_runtime_mark_last_busy(struct device *dev);
> > >      - set the power.last_busy field to the current time
> > >  