drm/i915/gt: Ensure that all new contexts clear STOP_RING

Set up the RING_MI_MODE in new contexts to clear the STOP_RING bit, just
in case they find it still set after a reset (as they are the first
contexts to be run).

Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk>
Reviewed-by: Matthew Auld <matthew.auld@intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20191229183153.3719869-1-chris@chris-wilson.co.uk

drivers/gpu/drm/i915/gt/intel_lrc.c

@@ -3030,10 +3030,8 @@ static void reset_csb_pointers(struct intel_engine_cs *engine)
 			       &execlists->csb_status[reset_value]);
 }
 
-static void __execlists_reset_reg_state(const struct intel_context *ce,
-					const struct intel_engine_cs *engine)
+static void __reset_stop_ring(u32 *regs, const struct intel_engine_cs *engine)
 {
-	u32 *regs = ce->lrc_reg_state;
 	int x;
 
 	x = lrc_ring_mi_mode(engine);
@@ -3043,6 +3041,14 @@ static void __execlists_reset_reg_state(const struct intel_context *ce,
 	}
 }
 
+static void __execlists_reset_reg_state(const struct intel_context *ce,
+					const struct intel_engine_cs *engine)
+{
+	u32 *regs = ce->lrc_reg_state;
+
+	__reset_stop_ring(regs, engine);
+}
+
 static void __execlists_reset(struct intel_engine_cs *engine, bool stalled)
 {
 	struct intel_engine_execlists * const execlists = &engine->execlists;
@@ -4043,6 +4049,8 @@ static void execlists_init_reg_state(u32 *regs,
 			     INTEL_GEN(engine->i915) >= 12 ?
 			     GEN12_CTX_BB_PER_CTX_PTR :
 			     CTX_BB_PER_CTX_PTR);
+
+	__reset_stop_ring(regs, engine);
 }
 
 static int