[Intel-gfx] drm/i915: Agressive downclocking on Baytrail

[Janne Heikkinen]

I've got Bay Trail based Asus X553MA and I've been experiencing daily hangs
with kernels beginning from 4.2-rc1. I haven't had any problems with 4.1.x
kernels and using 4.1.13 I've gotten constant 5+ day uptimes since November
(I had to at least suspend it once per week for traveling but during Christmas
longest uptime was 11 days).

Now I did bisection beginning with marking 4.2-rc1 as bad and 4.1.0 as good
and found out that it was this commit:

[8fb55197e64d5988ec57b54e973daeea72c3f2ff]
drm/i915: Agressive downclocking on Baytrail

causing the hangs.

4.4-rc8 hanged in less than hour. After I reversed the patch from it and
commented out lines containing related fields from i915_debugfs.c
I now seem to have stable 4.4-rc8.