linux-kernel - Re: [PATCH v10 3/5] amba: Don't unprepare the clocks if device driver wants IRQ safe runtime PM

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Message-ID: <1582300.GC6cj61ZAD@vostro.rjw.lan>
Date:	Sat, 08 Nov 2014 00:52:38 +0100
From:	"Rafael J. Wysocki" <rjw@...ysocki.net>
To:	Krzysztof Kozlowski <k.kozlowski@...sung.com>
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 3/5] amba: Don't unprepare the clocks if device driver wants IRQ safe runtime PM

On Friday, November 07, 2014 09:01:09 AM Krzysztof Kozlowski wrote:
> On czw, 2014-11-06 at 23:52 +0100, Rafael J. Wysocki wrote:
> > On Thursday, November 06, 2014 09:36:48 AM Krzysztof Kozlowski 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       | 17 +++++++++++++----
> > >  include/linux/amba/bus.h |  1 +
> > >  2 files changed, 14 insertions(+), 4 deletions(-)
> > > 
> > > diff --git a/drivers/amba/bus.c b/drivers/amba/bus.c
> > > index 47bbdc1b5be3..356f906c6966 100644
> > > --- a/drivers/amba/bus.c
> > > +++ b/drivers/amba/bus.c
> > > @@ -95,8 +95,14 @@ static int amba_pm_runtime_suspend(struct device *dev)
> > >  	struct amba_device *pcdev = to_amba_device(dev);
> > >  	int ret = pm_generic_runtime_suspend(dev);
> > >  
> > > -	if (ret == 0 && dev->driver)
> > > -		clk_disable_unprepare(pcdev->pclk);
> > > +	if (ret == 0 && dev->driver) {
> > > +		pcdev->irq_safe = dev->power.irq_safe;
> > > +
> > > +		if (pcdev->irq_safe)
> > > +			clk_disable(pcdev->pclk);
> > > +		else
> > > +			clk_disable_unprepare(pcdev->pclk);
> > > +	}
> > >  
> > >  	return ret;
> > >  }
> > > @@ -107,7 +113,10 @@ static int amba_pm_runtime_resume(struct device *dev)
> > >  	int ret;
> > >  
> > >  	if (dev->driver) {
> > > -		ret = clk_prepare_enable(pcdev->pclk);
> > > +		if (pcdev->irq_safe)
> > > +			ret = clk_enable(pcdev->pclk);
> > > +		else
> > > +			ret = clk_prepare_enable(pcdev->pclk);
> > >  		/* Failure is probably fatal to the system, but... */
> > >  		if (ret)
> > >  			return ret;
> > > @@ -115,7 +124,7 @@ static int amba_pm_runtime_resume(struct device *dev)
> > >  
> > >  	return pm_generic_runtime_resume(dev);
> > >  }
> > > -#endif
> > > +#endif /* CONFIG_PM */
> > >  
> > >  static const struct dev_pm_ops amba_pm = {
> > >  	.suspend	= pm_generic_suspend,
> > > diff --git a/include/linux/amba/bus.h b/include/linux/amba/bus.h
> > > index ac02f9bd63dc..c4bae79851fb 100644
> > > --- a/include/linux/amba/bus.h
> > > +++ b/include/linux/amba/bus.h
> > > @@ -32,6 +32,7 @@ struct amba_device {
> > >  	struct clk		*pclk;
> > >  	unsigned int		periphid;
> > >  	unsigned int		irq[AMBA_NR_IRQS];
> > > +	unsigned int		irq_safe:1;
> > 
> > Why do we need the new flag?  Seems redundant to me.
> 
> Some poorly written driver could set irq_safe somewhere between suspend
> and resume (e.g. in suspend callback).

It could also modify your bus type irq_safe flag to hide the fact.  In my
opinion, it doesn't really help.

Rafael

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