linux-kernel - Re: [PATCH] cpufreq: cpufreq-cpu0: Use a sane boot frequency when booting with a mismatched bootloader configuration

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Message-ID: <528B72C1.5060006@ti.com>
Date:	Tue, 19 Nov 2013 08:16:33 -0600
From:	Nishanth Menon <nm@...com>
To:	Viresh Kumar <viresh.kumar@...aro.org>,
	Shawn Guo <shawn.guo@...aro.org>
CC:	"Rafael J. Wysocki" <rjw@...ysocki.net>,
	"cpufreq@...r.kernel.org" <cpufreq@...r.kernel.org>,
	"linux-pm@...r.kernel.org" <linux-pm@...r.kernel.org>,
	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
	Carlos Hernandez <ceh@...com>
Subject: Re: [PATCH] cpufreq: cpufreq-cpu0: Use a sane boot frequency when
 booting with a mismatched bootloader configuration

On 11/18/2013 09:46 PM, Viresh Kumar wrote:
> On 19 November 2013 07:51, Shawn Guo <shawn.guo@...aro.org> wrote:
>> No, I did not say that.  IMO, when cpufreq-cpu0 sees a mismatch, it has
>> no way to know or assume which one is correct and which is incorrect.
>> The best thing it can do is to fail out without changing anything about
>> running frequency and voltage.
> 
> Not specifically on this patch, but this is what I feel about this issue:
> 
> - As we are discussing on the other thread, there is scope of adding
> "unknown" field in tables so that people would know that they were
> running out of table freq at some point..

Consider something like userspace governor selection -> the device at
boot will probably remain in an unknown/"invalid" configuration till
the very first transition attempt. I am less worried about the stats
than not following what the hardware description is (as stated by
device tree/other forms).

I staunchly disagree that at a point of mismatch detection, we just
refuse to load up cpufreq governor -even though we know from device
tree/other alternative entries what the hardware behavior is supposed
to be. To refuse to loadup to a known configuration is considering the
"valid configuration" data provided to the driver is wrong - an
equivalent(considering the i2c example) is that if i2c driver sees bus
configured for 3.4MHz and was asked to use 100KHz, it just refuses to
load up!

> - This is a common problem for all drivers/platforms and not only
> cpufreq-cpu0, so the solution has to be generic and not driver
> specific.. So, atleast I don't want to get this patch in at any cost,
> unless there is a generic solution present..
> - There are non-dt drivers as well, and so freq table is present
> with the kernel and we can't support all frequencies that bootloader
> may end up with..
The above two are fair comments -> but that implies that policy->cur
population should no longer be the responsibility of cpufreq drivers
and be the responsibility of cpufreq core. are we stating we want to
move that to cpufreq core?

-- 
Regards,
Nishanth Menon
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