linux-kernel - Re: [PATCH v2] i2c: s3c2410: dont need CPU

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Message-ID: <CAD=FV=XsZoGUeppkxMq9DnVsp761s6ckStsmUxR4aEL3U7JZ1A@mail.gmail.com>
Date:	Tue, 15 Oct 2013 08:38:32 -0700
From:	Doug Anderson <dianders@...omium.org>
To:	Kyungmin Park <kmpark@...radead.org>
Cc:	Naveen Krishna Chatradhi <ch.naveen@...sung.com>,
	"linux-i2c@...r.kernel.org" <linux-i2c@...r.kernel.org>,
	Tomasz Figa <t.figa@...sung.com>,
	Simon Glass <sjg@...omium.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	linux-samsung-soc <linux-samsung-soc@...r.kernel.org>,
	Wolfram Sang <wsa@...-dreams.de>,
	Ben Dooks <ben-linux@...ff.org>,
	Grant Likely <grant.likely@...retlab.ca>,
	"broonie@...nel.org" <broonie@...nel.org>,
	"cpgs ." <cpgs@...sung.com>
Subject: Re: [PATCH v2] i2c: s3c2410: dont need CPU_FREQ transitions for
 exynos series

Hi,

On Mon, Oct 14, 2013 at 11:56 PM, Kyungmin Park <kmpark@...radead.org> wrote:
> On Tue, Oct 15, 2013 at 3:23 PM, Naveen Krishna Chatradhi
> <ch.naveen@...sung.com> wrote:
>> For Exynos4 and Exynos5 SoCs from Samsung the 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 if CONFIG_CPU_FREQ_S3C24XX is enabled.
>>
>> This change should save a bunch of cpufreq transitions calls
>> which does not apply to exynos SoCs.
>>
>> Signed-off-by: Naveen Krishna Chatradhi <ch.naveen@...sung.com>
> Acked-by: Kyungmin Park <kyungmin.park@...sung.com>
>> ---
>> Changes since v1:
>> Use CONFIG_CPU_FREQ_S3C24XX instead of (CONFIG_CPU_FREQ & !CONFIG_EXYNOS)
>> As commented by Tomasz
>>
>>  drivers/i2c/busses/i2c-s3c2410.c |    4 ++--
>>  1 file changed, 2 insertions(+), 2 deletions(-)

Looks great to me.  Thank you for the suggestions Tomasz, as always.

Reviewed-by: Doug Anderson <dianders@...omium.org>

We need to come up with a solution for the CPU_FREQ stuff in
s3c2410_wdt too.  We could use a similar solution but since the
CPU_FREQ stuff in s3c2410_wdt is more than just an optimization it
means that it's not good if S3C24XX is included in a multiplatform
kernel.  (For the watchdog it's more than just an optimization since
every frequency transition actually pets the watchdog, making it
useless when you transition several times per second).

-Doug
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