Bug 25857

Summary: [945]: Entire screen "jerks" randomly after removing external monitor
Product: DRI Reporter: JR <zorael>
Component: DRM/IntelAssignee: Daniel Vetter <daniel>
Status: CLOSED INVALID QA Contact:
Severity: normal    
Priority: medium CC: ben, chris, daniel, jbarnes, torotil, zorael
Version: unspecified   
Hardware: x86 (IA32)   
OS: Linux (All)   
Whiteboard:
i915 platform: i915 features:

Description JR 2010-01-02 03:13:29 UTC 
Kubuntu 9.10, kernel 2.6.33rc2
Intel driver version 2.9.0 (package 2.9.0-1ubuntu2)
libdrm packages from xorg-edgers ppa, package versions 2.4.17+git20091230.c5c503b5-0ubuntu0sarvatt~karmic
Machine is an Advent 4211 netbook (MSI Wind U100 rebrand).

Behavior:
The screen randomly makes weird jerks where entire screen content is temporarily displaced for a split second (100ms perhaps). It's as if something briefly tugs at the screen at random intervals. The behavior starts after having disabled an external monitor and lasts until X session restart, until you reenable the other monitor, or if you start glxgears and keep it running in the background.

How to reproduce:
1. Connect an external monitor
2. Enable monitor, such as with 'xrandr --output VGA1 --mode 1280x1024 --above LVDS1'
3. Disable monitor with 'xrandr --output VGA1 --off'
4. Wait and observe screen jerks

How to recover:
- Restart X
OR
- Reenable monitor and keep it enabled
OR
- Run glxgears and keep it running in the background
Comment 1 JR 2010-01-02 03:40:25 UTC 
Correction; behavior persists even after X restart (complete stop/start). Reboot is necessary.

Please reassign this report if this falls outside of xorg/intel.
Comment 2 Carl Worth 2010-02-17 15:02:47 UTC 
This machine has a 945 GPU, right?

-Carl
Comment 3 JR 2010-02-17 17:14:26 UTC 
    $ lspci | grep VGA
    00:02.0 VGA compatible controller: Intel Corporation Mobile 945GME Express Integrated Graphics Controller (rev 03)

Apologies, I really should have included that in the original report.

As per advice from #intel-gfx on irc.freenode.net I added 'i915.powersave=0' as a bootline option, after which this behavior stopped. I have since installed Kubuntu 10.04 Lucid, and in its kernel (2.6.32) powersaving seems to be disabled by default, removing the need for the option.

When it was flickering, intel_gpu_top showed some process (framebuffer compression?) constantly maxing out at 99% - whereas now with powersaving disabled everything is hovering at near 0% at idle.

I imagine this is a duplicate of some much larger i915 bug?
Comment 4 Chris Wilson 2010-06-24 11:15:02 UTC 
The "jerk" is a FIFO underrun. The debugging that helps here is an intel_reg_dump before and after the jerks begin. Rebooting with drm.debug=0xf might be useful to record the timings and pixel clocks used when calculating the FIFO size.
Comment 5 Daniel Vetter 2012-11-13 13:26:06 UTC 
We need the debug output, but the reporter seems to be awol. Closing this, please reopen once you've gathered the requested information (reg dumps + dmesg with drm.debug=0xe).
Comment 6 JR 2012-11-13 15:02:53 UTC 
Reporter here. Many apologies for the lack of feedback.

The machine on which this happened is on the shelf counting electric sheep, so I haven't been able to casually debug it amid everyday use. Ever since I migrated to a beefier laptop it simply hasn't scratched my itch, so to speak, 

I'll try to find the time to bring said laptop back to life for some torture.
Comment 7 Daniel Vetter 2012-11-13 15:15:20 UTC 
Cool, thanks for the feedback. Please reopen this bug here once your machine is fit for testing - we're working on (finally) tackling the dsparb underrun problem for real, so might have a patch to test soon.

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