linux-kernel - Re: [PATCH Resend] cpufreq: remove sysfs files for CPU which failed to come back after resume

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Date:	Mon, 23 Dec 2013 11:57:12 +0100
From:	Bjørn Mork <bjorn@...k.no>
To:	Viresh Kumar <viresh.kumar@...aro.org>
Cc:	"Rafael J. Wysocki" <rjw@...ysocki.net>,
	"cpufreq\@vger.kernel.org" <cpufreq@...r.kernel.org>,
	"linux-pm\@vger.kernel.org" <linux-pm@...r.kernel.org>,
	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH Resend] cpufreq: remove sysfs files for CPU which failed to come back after resume

Viresh Kumar <viresh.kumar@...aro.org> writes:
> On 23 December 2013 14:53, Bjørn Mork <bjorn@...k.no> wrote:
>
>> But if you really want to implement suspend/resume, then you
>> do need to keep the whole device and not just the sysfs files. Keeping
>> the attribute files allow you to save and restore changed permissions,
>> but it doesn't save any user modified settings.
>
> Which settings are you talking about? I thought we are preserving all
> files..

I could be missing something, but I haven't noticed any attempt to
preserve anything except the sysfs files.

I tried modifying the max frequency, using

 echo 800000 >/sys/devices/system/cpu/cpu0/cpufreq/scaling_max_freq
 echo 800000 >/sys/devices/system/cpu/cpu1/cpufreq/scaling_max_freq

After supend + resume the boot CPU still had the modifed maximum, while
the non-boot core was reset to the default value.  I changed the gid of
both files too, verifying that they were saved and restored as expected.
But the value will change to default.

IMHO it would still be a lot better if this was handled as a true
hotplug event, allowing userspace to reset values/modes/owners on
resume. Hiding the hotplug event and saving part of the userspace
controlled environment is worse than not doing anything at all.

Bjørn
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