linux-kernel - Re: [RFC PATCH] cpufreq: cpufreq-cpu0: do not allow transitions with regulators suspended

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Message-ID: <CAKohpokz6YEqz8ZNmQ77y8K3qvKYu3ffgVmiEcDyh2M9FsDGPg@mail.gmail.com>
Date:	Fri, 15 Nov 2013 15:57:36 +0530
From:	Viresh Kumar <viresh.kumar@...aro.org>
To:	Nishanth Menon <nm@...com>
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>,
	Shawn Guo <shawn.guo@...aro.org>
Subject: Re: [RFC PATCH] cpufreq: cpufreq-cpu0: do not allow transitions with
 regulators suspended

On 14 November 2013 22:34, Nishanth Menon <nm@...com> wrote:
> I think it is still too early to do so :(

:)

> equivalent patch: http://pastebin.mozilla.org/3603467 (with minor
> changes for build)
>
> Basic tests: http://pastebin.mozilla.org/3603456 (governor is
> functional, but governor kicks in early before i2c is resumed)
>
> With call stack: http://pastebin.mozilla.org/3603455 to highlight call
> sequences
>
> Seems like we might want to pause governor as early in the suspend
> sequence as possible to allow SoC and regulator stuff to suspend
> themselves without cpufreq interfering.. just my 2 cents..

You made me spend a day on this :)
It wasn't a day's job really but I got into a really hard to crack bug with my
patch, I was calling __cpufreq_governor() from under write_lock_irqsave
for cpufreq_driver_lock. And __cpufreq_governor() had:

 read_lock_irqsave(&cpufreq_driver_lock, flags);

I wasn't able to suspend my system: ARM, X86.. It simply stopped
printing anything and I didn't had a clue of what's going on.. Hacked
everything possible, even kernel/power/suspend.c to return early
(yeah I used freezer > pm_test as well, but I wanted to return before
freezing userspace)...

Then somehow I got to know that this is the wrong piece of code :)

But probably I have a solution now to which you can't say:

"I think it is still too early to do so :("

:)

Give it a try and give a Tested-by please :)
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