[Intel-gfx] [PATCH 2/6] drm/i915: Trust programmed MCR in read_subslice_reg

[Chris Wilson]

Quoting Tvrtko Ursulin (2019-07-17 19:06:20)
> From: Tvrtko Ursulin <tvrtko.ursulin at intel.com>
> 
> Instead of re-calculating the MCR selector in read_subslice_reg do the
> rwm on its existing value and restore it when done.

I successfully worked back from implementation to changelog.
> 
> This consolidates MCR programming to one place for cnl+, and avoids
> re-calculating its default value on older platforms during hangcheck.
> 
> Signed-off-by: Tvrtko Ursulin <tvrtko.ursulin at intel.com>
Reviewed-by: Chris Wilson <chris at chris-wilson.co.uk>
-Chris