Nouveau - Feb 2015 - [Bug 89113] New: NVA8 constantly flickers when clocked to lowest pstate

https://bugs.freedesktop.org/show_bug.cgi?id=89113

            Bug ID: 89113
           Summary: NVA8 constantly flickers when clocked to lowest pstate
           Product: xorg
           Version: unspecified
          Hardware: x86-64 (AMD64)
                OS: Linux (All)
            Status: NEW
          Severity: normal
          Priority: medium
         Component: Driver/nouveau
          Assignee: nouveau at lists.freedesktop.org
          Reporter: charleszhang77 at gmail.com
        QA Contact: xorg-team at lists.x.org

Created attachment 113426
  --> https://bugs.freedesktop.org/attachment.cgi?id=113426&action=edit
VBIOS

with stock nouveau from kernel 3.19.0-1.fc22.x86_64

this nva8 came with a thinkpad t410

my pstate file looks like this: 
03: core 135 MHz shader 270 MHz memory 135 MHz
07: core 405 MHz shader 810 MHz memory 405 MHz
0f: core 606 MHz shader 1468 MHz memory 790 MHz
AC: core 405 MHz shader 810 MHz memory 405 MHz

when clocking to 07 or 0f everything works.
however, when clocking to pstate=03 i get constant flickering (maybe <5-10
hz),
although the clocks do change, and nothing crashes. (i can change clocks back
to 07 or 0f with no more flickering)

vbios attached

mmiodump where i fumbled around with powermizer while the blob reclocked
(no second monitor attached):
https://www.dropbox.com/s/jjh6hpcix1swc7r/mmiotrace.log?dl=0

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--- Comment #1 from C, Zhang <charleszhang77 at gmail.com> ---
there are no additional kernel messages when reclocking as well

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--- Comment #2 from C, Zhang <charleszhang77 at gmail.com> ---
Created attachment 113430
  --> https://bugs.freedesktop.org/attachment.cgi?id=113430&action=edit
PFB region peeks for pstate 07

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--- Comment #3 from Pierre Moreau <pierre.morrow at free.fr> ---
(In reply to C, Zhang from comment #0)
> however, when clocking to pstate=03 i get constant flickering (maybe
<5-10
> hz)
Flickering at low clocks is expected and is most likely due to hardware
constraints - memory not being quick enough to deal with the additional screen,
hence no flickering at higher clock - rather than a driver bug. Look in
nvidia-settings which clocks the blob sets when you plug your external screen
in: most likely it will automatically go from level 03 to level 07 and won't
go
back to 03 unless you unplug the external screen.
See "Blank monitor, flicker, snow, or other random live image
corruption" at
http://nouveau.freedesktop.org/wiki/TroubleShooting/#index8h3.

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--- Comment #4 from C, Zhang <charleszhang77 at gmail.com> ---
Right. That makes a lot of sense; unplugging an external monitor fixes the
issue. I guess it's just a hardware limitation then. The blob does indeed
avoid
03 with an extra monitor attached. Thanks for the help! That'd be another
thing
to worry about if dynamic power scaling were ever implemented for nouveau then.

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Pierre Moreau <pierre.morrow at free.fr> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
             Status|NEW                         |RESOLVED
         Resolution|---                         |NOTABUG

--- Comment #5 from Pierre Moreau <pierre.morrow at free.fr> ---
Closing this bug report as NOTABUG.
Feel free to reopen it if we forget about hardware limitations when adding
support for dynamic reclocking!

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