[Bug 109477] [regression, bisected] [i915] setting initial watermarks on gen 7 IVYBRIDGE causes blank lines on monitor

[bugzilla-daemon at freedesktop.org]

https://bugs.freedesktop.org/show_bug.cgi?id=109477

--- Comment #8 from Ville Syrjala <ville.syrjala at linux.intel.com> ---
(In reply to Andrea from comment #7)
> (In reply to Ville Syrjala from comment #6)
> > All the numbers look very much correct :/
> > 
> > Does the corruption go away if you start X (or whatever) that enables the
> > hardware cursor? The watermark dumps at least seemed to be w/o the cursor.
> 
> The corruption is present since boot-time, and stays there when the X
> starts. Sometimes it disappears (e.g., in response to a window/desktop
> switch), but in a non-deterministic way and the corruption comes back later.
> 
> > I see the BIOS is pretty old. Can you try to update it?
> 
> I will try in the next days, but from a first look it seems all updates
> require Windows (which I've not on this system).

Dunno if this is the right one, but some T431s seems to have ISOs available for
BIOS update:
https://download.lenovo.com/pccbbs/mobiles/ghuj20us.iso

> 
> > Let's also try to figure out which watermark level is the problem.
> > Please do these tests with drm-tip because it might not work with an older
> > kernel.
> > 
> > First let's rule out LP3:
> > # echo '12 4 16 0' > /sys/kernel/debug/dri/0/i915_pri_wm_latency
> > # echo '12 4 16 0' > /sys/kernel/debug/dri/0/i915_cur_wm_latency
> > $ xset dpms force off ; xset dpms force on
> > Still corrupted?
> 
> Yes
> 
> > Then LP2:
> > # echo '12 4 0 0' > /sys/kernel/debug/dri/0/i915_pri_wm_latency
> > # echo '12 4 0 0' > /sys/kernel/debug/dri/0/i915_cur_wm_latency
> > $ xset dpms force off ; xset dpms force on
> > Still corrupted?
> 
> Yes
> 
> > And finally LP1:
> > # echo '12 0 0 0' > /sys/kernel/debug/dri/0/i915_pri_wm_latency
> > # echo '12 0 0 0' > /sys/kernel/debug/dri/0/i915_cur_wm_latency
> > $ xset dpms force off ; xset dpms force on
> > Still corrupted?
> 
> No, the corruption is gone. Switching windows, desktops, focus etc seems to
> work fine. And it doesn't re-appear after > 10 mins.

Hmm. That machine seems very broken when even LP1 doesn't work.

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