drm/i915: Never fully mask the the EI up rps interrupt on SNB/IVB

drm/i915: Never fully mask the the EI up rps interrupt on SNB/IVB

commit a7b4667a00025ac28300737c868bd4818b6d8c4d upstream.

SNB (and IVB too I suppose) starts to misbehave if the GPU gets stuck
in an infinite batch buffer loop. The GPU apparently hogs something
critical and CPUs start to lose interrupts and whatnot. We can keep
the system limping along by unmasking some interrupts in
GEN6_PMINTRMSK. The EI up interrupt has been previously chosen for
that task, so let's never mask it.

v2: s/gen6_rps_pm_mask/gen6_sanitize_rps_pm_mask/ (Chris)

Bugzilla: https://bugs.freedesktop.org/show_bug.cgi?id=93122
Signed-off-by: Ville Syrjälä <ville.syrjala@linux.intel.com>
Reviewed-by: Chris Wilson <chris@chris-wilson.co.uk>
Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk>
Link: http://patchwork.freedesktop.org/patch/msgid/1464014568-4529-1-git-send-email-ville.syrjala@linux.intel.com
(cherry picked from commit 12c100bfa5d9103b6c4d43636fee09c31e75605a)
Signed-off-by: Daniel Vetter <daniel.vetter@ffwll.ch>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>