Bug 89113

Summary: NVA8 constantly flickers when clocked to lowest pstate
Product: xorg Reporter: C, Zhang <charleszhang77>
Component: Driver/nouveauAssignee: Nouveau Project <nouveau>
Status: RESOLVED NOTABUG QA Contact: Xorg Project Team <xorg-team>
Severity: normal    
Priority: medium    
Version: unspecified   
Hardware: x86-64 (AMD64)   
OS: Linux (All)   
Whiteboard:
i915 platform: i915 features:
Attachments:
Description Flags
VBIOS
none
PFB region peeks for pstate 07 none

Description C, Zhang 2015-02-13 00:38:59 UTC 
Created attachment 113426 [details]
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
Comment 1 C, Zhang 2015-02-13 00:40:29 UTC 
there are no additional kernel messages when reclocking as well
Comment 2 C, Zhang 2015-02-13 01:18:13 UTC 
Created attachment 113430 [details]
PFB region peeks for pstate 07
Comment 3 Pierre Moreau 2015-02-13 10:06:13 UTC 
(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.
Comment 4 C, Zhang 2015-02-13 22:53:01 UTC 
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.
Comment 5 Pierre Moreau 2015-02-19 09:05:16 UTC 
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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