linux-kernel - Re: [PATCH] ARM: smp_twd: Reconfigure clockevents after cpufreq change

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Date:	Tue, 17 May 2011 10:06:07 -0700
From:	Colin Cross <ccross@...roid.com>
To:	Santosh Shilimkar <santosh.shilimkar@...com>
Cc:	linux-arm-kernel@...ts-infradead.org,
	Thomas Gleixner <tglx@...utronix.de>,
	Russell King <linux@....linux.org.uk>,
	Rob Herring <robherring2@...il.com>,
	linux-arm-kernel@...ts.infradead.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH] ARM: smp_twd: Reconfigure clockevents after cpufreq change

On Tue, May 17, 2011 at 7:00 AM, Santosh Shilimkar
<santosh.shilimkar@...com> wrote:
> Colin,
>
> On 5/17/2011 4:51 AM, Colin Cross wrote:
>>
>> The localtimer's clock changes with the cpu clock.  After a
>> cpufreq transition, update the clockevent's frequency and
>> reprogram the next clock event.
>>
>> Adds a clock called "smp_twd" that is used to determine the
>> twd frequency, which can also be used at init time to
>> avoid calibrating the twd frequency.
>>
>> Signed-off-by: Colin Cross<ccross@...roid.com>
>> Cc: Thomas Gleixner<tglx@...utronix.de>
>> Cc: Russell King<linux@....linux.org.uk>
>> Cc: Santosh Shilimkar<santosh.shilimkar@...com>
>> Cc: Rob Herring<robherring2@...il.com>
>> ---
>>  arch/arm/kernel/smp_twd.c |   69
>> +++++++++++++++++++++++++++++++++++++++++++--
>>  1 files changed, 66 insertions(+), 3 deletions(-)
>>
>> This patch depends on Thomas Gleixner's patch to add
>> clockevents_reconfigure
>> See: https://lkml.org/lkml/2011/5/13/122
>>
>> This patch adds a clock that can be used to skip calibration as well
>> as update the frequency.  A later patch (or a later version of this patch)
>> will drop twd_calibrate_rate once all platforms provide the necessary
>> smp_twd clock.
>>
>
> Since the "smp_twd" clock node will not have a clk_set_rate()
> associated with it, will the clk_get_rate() gives you real
> rate. May be we can associate this node as a child of
> CPU clock node and use the fixed divider based on peripheral
> ratio. Is that the idea here to realize it ?

Yes, the idea is that it will be a fixed divider off the cpu clock,
which will have been updated by cpufreq.
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