linux-kernel - Re: [PATCH v9 2/4] amba: Don't unprepare the clocks if device driver wants IRQ safe runtime PM

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Date:	Wed, 05 Nov 2014 09:48:56 +0100
From:	Krzysztof Kozlowski <k.kozlowski@...sung.com>
To:	Ulf Hansson <ulf.hansson@...aro.org>
Cc:	"Rafael J. Wysocki" <rjw@...ysocki.net>,
	Len Brown <len.brown@...el.com>, Pavel Machek <pavel@....cz>,
	Jonathan Corbet <corbet@....net>,
	Russell King <linux@....linux.org.uk>,
	Dan Williams <dan.j.williams@...el.com>,
	Vinod Koul <vinod.koul@...el.com>,
	Alan Stern <stern@...land.harvard.edu>,
	"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 v9 2/4] amba: Don't unprepare the clocks if device driver
 wants IRQ safe runtime PM

On wto, 2014-11-04 at 20:06 +0100, Ulf Hansson wrote:
> On 4 November 2014 13:52, Krzysztof Kozlowski <k.kozlowski@...sung.com> wrote:
> > The AMBA bus driver defines runtime Power Management functions which
> > disable and unprepare AMBA bus clock. This is problematic for runtime PM
> > because unpreparing a clock might sleep so it is not interrupt safe.
> >
> > However some drivers may want to implement runtime PM functions in
> > interrupt-safe way (see pm_runtime_irq_safe()). In such case the AMBA
> > bus driver should only disable/enable the clock in runtime suspend and
> > resume callbacks.
> >
> > Detect the device driver behavior during runtime suspend. During runtime
> > resume deal with clocks according to stored value.
> >
> > Signed-off-by: Krzysztof Kozlowski <k.kozlowski@...sung.com>
> > ---
> >  drivers/amba/bus.c       | 24 ++++++++++++++++++++----
> >  include/linux/amba/bus.h |  1 +
> >  2 files changed, 21 insertions(+), 4 deletions(-)
> >
> > diff --git a/drivers/amba/bus.c b/drivers/amba/bus.c
> > index 47bbdc1b5be3..27ec8882ec8e 100644
> > --- a/drivers/amba/bus.c
> > +++ b/drivers/amba/bus.c
> > @@ -85,6 +85,13 @@ static struct device_attribute amba_dev_attrs[] = {
> >  };
> >
> >  #ifdef CONFIG_PM
> > +
> > +#ifdef CONFIG_PM_RUNTIME
> > +#define get_pm_runtime_irq_safe(dev)   ((dev)->power.irq_safe)
> > +#else
> > +#define get_pm_runtime_irq_safe(dev)   1
> 
> No, this doesn't work for those drivers that isn't configured as
> irq_safe. The pm_runtime_force_suspend() invoked from the driver's
> system PM suspend callback, will expect clocks to be unprepared when
> CONFIG_PM_RUNTIME is unset.

D'oh! You're right... 

> To address this issue, in principle we need to know whether the driver
> has invoked pm_runtime_irq_safe(), even when CONFIG_PM_RUNTIME is
> unset.
> 
> This may be solved by the help of PM core:
> 1) Move the irq_safe member in the struct dev_pm_info, outside the
> #ifdef CONFIG_PM_RUNTIME.
> 2) Let the pm_runtime_irq_safe() function be implemented for CONFIG_PM
> instead of CONFIG_PM_RUNTIME.

Before I'll start implementing this - could PM maintainers share their
opinion on such change?

Best regards,
Krzysztof


> If the PM core maintainers don't like that approach we can always add
> an amba specific wrapper function for pm_runtime_irq_safe() and store
> the information needed in the struct amba_device.
> 
> Kind regards
> Uffe


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