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    SubjectRe: unparseable, undocumented /sys/class/drm/.../pstate
    On Sun, Jun 22, 2014 at 10:12:14PM -0400, Ilia Mirkin wrote:
    > On Sat, Jun 21, 2014 at 3:45 PM, Greg KH <greg@kroah.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@ucw.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?
    > >> >
    > >> > Thanks,
    > >> > Pavel
    > >> >
    > >> > PS: I have no nvidia, got the news at
    > >> >
    > >> > http://www.phoronix.com/scan.php?page=article&item=nouveau_try_linux316&num=2
    > >>
    > >> 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
    > >> 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?
    > >
    > > Yes, please move it to debugfs.
    >
    > Could we just say that the format of this file is one-per-line of
    >
    > level: information-for-the-user
    >
    > 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.

    sysfs files are "one value per file", that's it. Do anything other than
    that, and it can not be in sysfs, sorry.

    greg k-h


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