[Intel-gfx] [PATCH] drm/i915: Empty the ring before disabling

[Chris Wilson]

Quoting Ville Syrjälä (2017-10-27 12:27:59)
> On Fri, Oct 27, 2017 at 12:56:39AM +0100, Chris Wilson wrote:
> > An interesting snippet from Sandybridge's prm:
> > 
> > "Although a Ring Buffer can be enabled in the non-empty state, it must
> > not be disabled unless it is empty. Attempting to disable a Ring Buffer
> > in the non-empty state is UNDEFINED."
> 
> However elsewhere it still says:
> "Writing the Head Offset while the RB is enabled is UNDEFINED"
> and
> "It can be enabled or disabled regardless of whether there
>  are valid instructions pending."

Nothing like a catch 22. Let's just reset the GPU first... 
-Chris