linux-kernel - Re: [PATCH 6/6 v6] cpufreq, highbank: add support for highbank cpufreq

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Message-ID: <50B6273B.1000007@calxeda.com>
Date:	Wed, 28 Nov 2012 09:01:15 -0600
From:	Mark Langsdorf <mark.langsdorf@...xeda.com>
To:	Shawn Guo <shawn.guo@...aro.org>
CC:	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	"cpufreq@...r.kernel.org" <cpufreq@...r.kernel.org>,
	"linux-pm@...r.kernel.org" <linux-pm@...r.kernel.org>,
	"linux-arm-kernel@...ts.infradead.org" 
	<linux-arm-kernel@...ts.infradead.org>,
	"devicetree-discuss@...ts.ozlabs.org" 
	<devicetree-discuss@...ts.ozlabs.org>
Subject: Re: [PATCH 6/6 v6] cpufreq, highbank: add support for highbank cpufreq

On 11/28/2012 09:17 AM, Shawn Guo wrote:
> On Wed, Nov 28, 2012 at 10:58:02PM +0800, Shawn Guo wrote:
>> On Wed, Nov 28, 2012 at 07:16:12AM -0600, Mark Langsdorf wrote:
>>> I'd
>>> have to move most of the logic of hb_set_target() into
>>> clk_highbank.c:clk_pll_set_rate() and then add extra logic for when
>>> cpufreq is not enabled/loaded.
>>
>> You only need to move hb_voltage_change() into cpu clock's .set_rate()
>> hook with no need of checking if cpufreq is enabled or not.
>>
> Need to also check whether frequency or voltage should be changed first
> in .set_rate() though.

Yes, that's entirely what I meant when I said that I would need to move
most of the hb_set_target() logic into .set_rate(). I would also need to
account for retries if the voltage set operation fails, which it
sometimes does.

The ECME handles changing the voltage but doesn't look like a voltage
regulator. Amongst other things, by design it doesn't export meaningful
voltage information to Linux. I tried to get cpufreq-clk0 to work with
the Highbank design and it ended up being much easier and more sane to
create a separate driver.

--Mark Langsdorf
Calxeda, Inc.

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