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

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Date:	Mon, 23 Jun 2014 09:29:51 -0400
From:	Ilia Mirkin <imirkin@...m.mit.edu>
To:	Pavel Machek <pavel@....cz>
Cc:	Greg KH <greg@...ah.com>,
	kernel list <linux-kernel@...r.kernel.org>,
	Ben Skeggs <bskeggs@...hat.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 Mon, Jun 23, 2014 at 9:02 AM, Pavel Machek <pavel@....cz> wrote:
> On Sun 2014-06-22 22:12:14, Ilia Mirkin wrote:
>> On Sat, Jun 21, 2014 at 3:45 PM, Greg KH <greg@...ah.com> wrote:
>> > On Sat, Jun 21, 2014 at 02:22:59PM -0400, 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.
>> >> >
>> >> > Should we disable it for now, so that userspace does not start
>> >> > depending on it and we'll not have to maintain it forever?
>> >> >
>> >> > I guess better interface would be something like
>> >> >
>> >> > pstate/07/core_clock_min
>> >> >           core_clock_max
>> >> >           memory_clock_min
>> >> >           memory_clock_max
>> >> >
>> >> > and then pstate/active containing just the number of active state?
>
>> Could we just say that the format of this file is one-per-line of
>>
>> level: information-for-the-user
>
> But it is not.

But it is...

> Management tools will want to parse it, sooner or
> later.  What is wrong with solution described above?

It is complex and annoying to the people that will actually use it.

>
>> And you can echo a level into it to switch to that level? That seems
>> like a reasonable ABI to have... would be happy to throw it into a
>> file somewhere... not sure where though.
>
> Documentation/ABI/testing/

Yes, I got that far. And then I became confused.

  -ilia
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