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From: "Rafael J. Wysocki" <rjw@sisk.pl>
To: Guenter Roeck <linux@roeck-us.net>
Subject: Re: [PATCH 4/4][update] hwmon / exynos4_tmu: Use struct dev_pm_ops for power management
Date: Sun, 8 Jul 2012 22:46:12 +0200
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Cc: LKML <linux-kernel@vger.kernel.org>,
        Linux PM list <linux-pm@vger.kernel.org>,
        Hans de Goede <hdegoede@redhat.com>,
        Alistair John Strachan <alistair@devzero.co.uk>,
        lm-sensors@lm-sensors.org, Jean Delvare <khali@linux-fr.org>,
        Kukjin Kim <kgene.kim@samsung.com>
References: <201207072302.16491.rjw@sisk.pl> <201207082148.15674.rjw@sisk.pl> <20120708203004.GA20390@roeck-us.net>
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On Sunday, July 08, 2012, Guenter Roeck wrote:
> On Sun, Jul 08, 2012 at 09:48:15PM +0200, Rafael J. Wysocki wrote:
> > From: Rafael J. Wysocki <rjw@sisk.pl>
> > 
> Hi Rafael,
> 
> > Make the Exynos4 TMU driver define its PM callbacks through
> > a struct dev_pm_ops object rather than by using legacy PM hooks
> > in struct platform_driver.
> > 
> > Signed-off-by: Rafael J. Wysocki <rjw@sisk.pl>
> > ---
> >  drivers/hwmon/exynos4_tmu.c |   18 +++++++++++-------
> >  1 file changed, 11 insertions(+), 7 deletions(-)
> > 
> > Index: linux/drivers/hwmon/exynos4_tmu.c
> > ===================================================================
> > --- linux.orig/drivers/hwmon/exynos4_tmu.c
> > +++ linux/drivers/hwmon/exynos4_tmu.c
> > @@ -476,34 +476,38 @@ static int __devexit exynos4_tmu_remove(
> >  }
> >  
> >  #ifdef CONFIG_PM
> > -static int exynos4_tmu_suspend(struct platform_device *pdev, pm_message_t state)
> > +static int exynos4_tmu_suspend(struct device *dev)
> >  {
> > -	exynos4_tmu_control(pdev, false);
> > +	exynos4_tmu_control(to_platform_device(dev), false);
> >  
> >  	return 0;
> >  }
> >  
> > -static int exynos4_tmu_resume(struct platform_device *pdev)
> > +static int exynos4_tmu_resume(struct device *dev)
> >  {
> > +	struct platform_device *pdev = to_platform_device(dev);
> > +
> >  	exynos4_tmu_initialize(pdev);
> >  	exynos4_tmu_control(pdev, true);
> >  
> >  	return 0;
> >  }
> > +
> > +static SIMPLE_DEV_PM_OPS(exynos4_tmu_pm,
> > +			 exynos4_tmu_suspend, exynos4_tmu_resume);
> > +#define EXYNOS4_TMU_PM	(&exynos4_tmu_pm)
> >  #else
> > -#define exynos4_tmu_suspend NULL
> > -#define exynos4_tmu_resume NULL
> > +#define EXYNOS4_TMU_PM	NULL
> >  #endif
> 
> Actually, looking into other drivers, the common approach seems to be to declare
> 
> static SIMPLE_DEV_PM_OPS(exynos4_tmu_pm,
> 			 exynos4_tmu_suspend, exynos4_tmu_resume);
> 
> outside the #ifdef code and then just assign
> 
> 		.pm = &exynos4_tmu_pm;
> 
> unconditionally.
> 
> That seems to be a much simpler solution. Any special reason for not
> implementing it this way ? Same question applies to the other patches in the
> series.

In fact, there are two ways.  One of them is what you said, the other is to
put SIMPLE_DEV_PM_OPS() under the #ifdef like I did.  I'm not sure which one
is prevalent, but what I did has the advatnage that the kernel data will
be slightly smaller if CONFIG_PM is unset.

Thanks,
Rafael