linux-kernel - Re: [PATCH] i2c: s3c2410: dont need CPU

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Date:	Sat, 12 Oct 2013 07:42:52 +0200
From:	Tomasz Figa <t.figa@...sung.com>
To:	Naveen Krishna Chatradhi <ch.naveen@...sung.com>
Cc:	sjg@...omium.org, linux-i2c@...r.kernel.org,
	linux-kernel@...r.kernel.org, linux-samsung-soc@...r.kernel.org,
	wsa@...-dreams.de, khali@...ux-fr.org, ben-linux@...ff.org,
	grant.likely@...retlab.ca, naveenkrishna.ch@...il.com,
	broonie@...nel.org, dianders@...omium.org, cpgs@...sung.com
Subject: Re: [PATCH] i2c: s3c2410: dont need CPU_FREQ transitions for exynos
 series

On Saturday 12 of October 2013 04:28:51 Tomasz Figa wrote:
> [Fixing incorrent mail addresses and dropping the old DT ML.]
> 
> On Saturday 12 of October 2013 04:22:04 Tomasz Figa wrote:
> > Hi Naveen,
> > 
> > On Friday 11 of October 2013 16:56:54 Naveen Krishna Chatradhi wrote:
> > > The exynos5 i2c clock is based on a fixed 66 MHz peripheral clock, and
> > > therefore is completely independent of the cpu frequency.
> > > Thus, registering for a CPU freq notifier is very wasteful.
> > > 
> > > This patch modifes the code such that, i2c bus registers to
> > > cpu_freq_transition only for non Exynos SoCs.
> > > 
> > > This change should save a bunch of cpufreq transitions calls
> > > which does not apply to exynos SoCs.
> > 
> > The idea is fine, although...
> > 
> > > Signed-off-by: Naveen Krishna Chatradhi <ch.naveen@...sung.com>
> > > ---
> > >  drivers/i2c/busses/i2c-s3c2410.c |    4 ++--
> > >  1 file changed, 2 insertions(+), 2 deletions(-)
> > > 
> > > diff --git a/drivers/i2c/busses/i2c-s3c2410.c b/drivers/i2c/busses/i2c-s3c2410.c
> > > index cab1c91..d062fa7 100644
> > > --- a/drivers/i2c/busses/i2c-s3c2410.c
> > > +++ b/drivers/i2c/busses/i2c-s3c2410.c
> > > @@ -123,7 +123,7 @@ struct s3c24xx_i2c {
> > >  	struct s3c2410_platform_i2c	*pdata;
> > >  	int			gpios[2];
> > >  	struct pinctrl          *pctrl;
> > > -#ifdef CONFIG_CPU_FREQ
> > > +#if defined(CONFIG_CPU_FREQ) && !defined(CONFIG_ARCH_EXYNOS)
> > 
> > ...this is not a good coding practice, especially when already having
> > multiplatform kernels in sight.
> > 
> > The best way would be to check on which SoC we are running at runtime,
> > but since this might need changing a lot of code, then at least I would
> > change this from !defined(EXYNOS) to defined(S3C24XX), so it is not being
> > compiled in when S3C24XX support is not enabled and if it's enabled then
> > the notifier will be registered as a safe fallback that will run correctly
> > on all platforms.

Actually you can simply check for CONFIG_CPU_FREQ_S3C24XX here.

Best regards,
Tomasz

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