[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

Andrea <andreatclist at gmail.com> changed:

           What    |Removed                     |Added
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             Status|NEEDINFO                    |NEW

--- Comment #7 from Andrea <andreatclist at gmail.com> ---
(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).

> 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.

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