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

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Message-id: <2030813.WOPcW68yit@amdn883>
Date:	Sat, 12 Oct 2013 04:28:51 +0200
From:	Tomasz Figa <t.figa@...sung.com>
To:	Naveen Krishna Chatradhi <ch.naveen@...sung.com>, sjg@...omium.org
Cc:	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

[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.
> 
> Best regards,
> Tomasz
> 
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