[Intel-gfx] [PATCH] drm/i915/gen11: enable support for headerless msgs

[Chris Wilson]

Quoting Dongwon Kim (2019-04-23 20:05:03)
> set bit5 (Headerless Message for Pre-emptable Contexts) in SAMPLER_MODE
> register while initializing render ring to enable support for headerless
> messages for preemptable GPGPU contexts on Gen11.

See icl_ctx_workarounds_init() and explain why we must set the default
value as userspace is already given access to SAMPLER_MODE. Does
changing the default break other workloads?
-Chris