linux-kernel - Re: [PATCH] clk: mediatek: Export CPU mux clocks for CPU frequency control

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Message-ID: <CAKohpo=90YH3TLfnMro0AQOM6_uMB_SPS9Q3j6Myz4RqqBdVHg@mail.gmail.com>
Date:	Thu, 5 Mar 2015 16:32:06 +0530
From:	Viresh Kumar <viresh.kumar@...aro.org>
To:	Sascha Hauer <s.hauer@...gutronix.de>,
	Russell King - ARM Linux <linux@....linux.org.uk>
Cc:	Pi-Cheng Chen <pi-cheng.chen@...aro.org>,
	Mark Rutland <mark.rutland@....com>,
	James Liao <jamesjj.liao@...iatek.com>,
	Linaro Kernel Mailman List <linaro-kernel@...ts.linaro.org>,
	Mike Turquette <mturquette@...aro.org>,
	Pawel Moll <pawel.moll@....com>,
	Ian Campbell <ijc+devicetree@...lion.org.uk>,
	Stephen Boyd <sboyd@...eaurora.org>,
	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
	Henry Chen <henryc.chen@...iatek.com>,
	Chen Fan <fan.chen@...iatek.com>,
	"devicetree@...r.kernel.org" <devicetree@...r.kernel.org>,
	Rob Herring <robh+dt@...nel.org>,
	linux-mediatek@...ts.infradead.org,
	Kumar Gala <galak@...eaurora.org>,
	Matthias Brugger <matthias.bgg@...il.com>,
	"Joe.C" <yingjoe.chen@...iatek.com>,
	Eddie Huang <eddie.huang@...iatek.com>,
	"linux-arm-kernel@...ts.infradead.org" 
	<linux-arm-kernel@...ts.infradead.org>
Subject: Re: [PATCH] clk: mediatek: Export CPU mux clocks for CPU frequency control

On 5 March 2015 at 16:21, Sascha Hauer <s.hauer@...gutronix.de> wrote:
> Given the variance of different SoCs I don't think it makes sense
> to try to handle all these cases. Instead the cpufreq-dt driver
> should just call clk_set_rate() on the CPU clock with the desired
> target frequency. Everything else should be handled in the clock
> driver which has intimate knowledge about the SoC anyway.

I agree..

@Russell: I wanted to ask you this since sometime..

On CPU-freq changes we fire PRE/POST notifiers and they are
used for updating loops_per_jiffies which then controls delays.

Now, it is fine to do that for normal frequencies, but what should be
the approach for intermediate frequencies ?

Intermediate freqs: On some platforms changing PLL's straight away
isn't considered safe and so we switch parent to another stable clock,
change PLL rate and switch back.

The *wild* thought I earlier had was to fire these notifiers for even these
intermediate frequencies, otherwise some of the delays will end before
they should have and that *might* cause other problems.

I wanted to know what do you (and other champs) think about this..

Thanks in advance for your advice.
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