drm/i915: Add information needed to track engine preempt state

We shouldn't inspect ELSP context status (or any other bits depending on
specific submission backend) when using GuC submission.
Let's use another piece of HWSP for preempt context, to write its bit of
information, meaning that preemption has finished, and hardware is now
idle.
Signed-off-by: Michał Winiarski <michal.winiarski@intel.com>
Cc: Chris Wilson <chris@chris-wilson.co.uk>
Cc: Jeff McGee <jeff.mcgee@intel.com>
Cc: Michal Wajdeczko <michal.wajdeczko@intel.com>
Cc: Oscar Mateo <oscar.mateo@intel.com>
Reviewed-by: Chris Wilson <chris@chris-wilson.co.uk>
Reviewed-by: Jeff McGee <jeff.mcgee@intel.com>
Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk>
Link: https://patchwork.freedesktop.org/patch/msgid/20171025200020.16636-9-michal.winiarski@intel.com

drivers/gpu/drm/i915/intel_ringbuffer.h

@@ -626,6 +626,8 @@ intel_write_status_page(struct intel_engine_cs *engine, int reg, u32 value)
  */
 #define I915_GEM_HWS_INDEX		0x30
 #define I915_GEM_HWS_INDEX_ADDR (I915_GEM_HWS_INDEX << MI_STORE_DWORD_INDEX_SHIFT)
+#define I915_GEM_HWS_PREEMPT_INDEX	0x32
+#define I915_GEM_HWS_PREEMPT_ADDR (I915_GEM_HWS_PREEMPT_INDEX << MI_STORE_DWORD_INDEX_SHIFT)
 #define I915_GEM_HWS_SCRATCH_INDEX	0x40
 #define I915_GEM_HWS_SCRATCH_ADDR (I915_GEM_HWS_SCRATCH_INDEX << MI_STORE_DWORD_INDEX_SHIFT)
 
@@ -778,6 +780,11 @@ static inline u32 intel_hws_seqno_address(struct intel_engine_cs *engine)
 	return engine->status_page.ggtt_offset + I915_GEM_HWS_INDEX_ADDR;
 }
 
+static inline u32 intel_hws_preempt_done_address(struct intel_engine_cs *engine)
+{
+	return engine->status_page.ggtt_offset + I915_GEM_HWS_PREEMPT_ADDR;
+}
+
 /* intel_breadcrumbs.c -- user interrupt bottom-half for waiters */
 int intel_engine_init_breadcrumbs(struct intel_engine_cs *engine);