3.15-rc2: i915 regression: only top 20% of screen works in X

[Daniel Vetter]

On Thu, Apr 24, 2014 at 7:50 AM, Chris Wilson <chris at chris-wilson.co.uk> wrote:
> That says that i915.ko failed to initialise the GPU (or rather the GPU
> wasn't responding) and bailed during module load. The key line here is
>
> [drm:init_ring_common] *ERROR* render ring initialization failed ctl
> 0001f001 head 00002034 tail 00000000 start 0012f000
>
> Jiri has been seeing a similar issue creep in during resume, but it is
> not reliable enough to bisect. Is your boot failure reliable enough to
> bisect? Also drm-intel-nightly should mitigate this failure and allow
> i915.ko to continue to load and run X, which would be worth testing to
> make sure that works as intended.

Oh right, g4x going beserk :( Apparently something changed in 3.15
somewhere which made this much more likely, but like Chris said in
Jiri's case it's too unreliable to reproduce for a bisect. We've had
this come&go pretty much ever since kms support was merged and never
tracked it down.

The bug is https://bugs.freedesktop.org/show_bug.cgi?id=76554

Like Chris said please test latest drm-intel-nighlty from
http://cgit.freedesktop.org/drm-intel to make sure that the recently
merged mitigation measures work properly. But those won't get your gpu
back, only the display and it's only for 3.16. We're still hunting a
proper fix for 3.15.

And if you can indeed reliably reproduce this a bisect could be really useful.
-Daniel
-- 
Daniel Vetter
Software Engineer, Intel Corporation
+41 (0) 79 365 57 48 - http://blog.ffwll.ch