linux-kernel - Re: unparseable, undocumented /sys/class/drm/.../pstate

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Date:	Sat, 21 Jun 2014 15:34:54 -0400
From:	Ilia Mirkin <imirkin@...m.mit.edu>
To:	Pavel Machek <pavel@....cz>
Cc:	kernel list <linux-kernel@...r.kernel.org>,
	Ben Skeggs <bskeggs@...hat.com>, Greg KH <greg@...ah.com>,
	Alexandre Courbot <acourbot@...dia.com>,
	David Airlie <airlied@...ux.ie>,
	"dri-devel@...ts.freedesktop.org" <dri-devel@...ts.freedesktop.org>
Subject: Re: unparseable, undocumented /sys/class/drm/.../pstate

On Sat, Jun 21, 2014 at 2:50 PM, Pavel Machek <pavel@....cz> wrote:
> On Sat 2014-06-21 14:22:59, Ilia Mirkin wrote:
>> On Sat, Jun 21, 2014 at 2:02 PM, Pavel Machek <pavel@....cz> wrote:
>> > Hi!
>> >
>> > AFAICT, pstate file will contain something like
>> >
>> > 07: core 100 MHz memory 123 MHz *
>> > 08: core 100-200 MHz memory 123 MHz
>> >
>> > ...which does not look exactly like one-value-per-file, and I'm pretty
>> > sure userspace will get it wrong if it tries to parse it. Plus, I
>> > don't see required documentation in Documentation/ABI.
> ...
>>
>> FTR, this file has been in place since 3.13, and there was a different
>> file before it (performance_levels), with a comparable format since
>> much earlier (definitely 3.8, probably earlier). I think it's meant
>> a
>
> According to the article, it is only starting to work now. I know
> articles can be wrong, but I don't have that hardware... Sorry if it
> is the case.

Commit 26fdd78cce3f51a49e1f2d3ad27ee893a28d220e introduced this particular one.
Commit 330c5988ee78045e6a731c3693251aaa5b0d14e3 had introduced the
former version, which was removed in 3.13, replaced with the new one.

>
>> lot more for people looking at it and echo'ing stuff to it to modify
>> the levels (where supported), than for programs parsing it. Perhaps
>> sysfs is the wrong place for this -- what is the right place? debugfs?
>
> debugfs would work, yes.
>                                                                         Pavel
> --
> (english) http://www.livejournal.com/~pavelmachek
> (cesky, pictures) http://atrey.karlin.mff.cuni.cz/~pavel/picture/horses/blog.html
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