drm/i915/execlists: Clear STOP_RING bit on reset

During reset, we try to ensure no forward progress of the CS prior to
the reset by setting the STOP_RING bit in RING_MI_MODE. Since gen9, this
register is context saved and do we end up in the odd situation where we
save the STOP_RING bit and so try to stop the engine again immediately
upon resume. This is quite unexpected and causes us to complain about an
early CS completion event!

Bugzilla: https://bugs.freedesktop.org/show_bug.cgi?id=111514Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk>
Cc: Mika Kuoppala <mika.kuoppala@linux.intel.com>
Reviewed-by: Mika Kuoppala <mika.kuoppala@linux.intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20190910080208.4223-1-chris@chris-wilson.co.uk

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

@@ -2368,6 +2368,17 @@ static struct i915_request *active_request(struct i915_request *rq)
 	return active;
 }
 
+static void __execlists_reset_reg_state(const struct intel_context *ce,
+					const struct intel_engine_cs *engine)
+{
+	u32 *regs = ce->lrc_reg_state;
+
+	if (INTEL_GEN(engine->i915) >= 9) {
+		regs[GEN9_CTX_RING_MI_MODE + 1] &= ~STOP_RING;
+		regs[GEN9_CTX_RING_MI_MODE + 1] |= STOP_RING << 16;
+	}
+}
+
 static void __execlists_reset(struct intel_engine_cs *engine, bool stalled)
 {
 	struct intel_engine_execlists * const execlists = &engine->execlists;
@@ -2455,6 +2466,7 @@ static void __execlists_reset(struct intel_engine_cs *engine, bool stalled)
 	GEM_TRACE("%s replay {head:%04x, tail:%04x\n",
 		  engine->name, ce->ring->head, ce->ring->tail);
 	intel_ring_update_space(ce->ring);
+	__execlists_reset_reg_state(ce, engine);
 	__execlists_update_reg_state(ce, engine);
 	mutex_release(&ce->pin_mutex.dep_map, 0, _THIS_IP_);
 

drivers/gpu/drm/i915/gt/intel_lrc_reg.h

@@ -39,6 +39,8 @@
 #define CTX_R_PWR_CLK_STATE		0x42
 #define CTX_END				0x44
 
+#define GEN9_CTX_RING_MI_MODE		0x54
+
 /* GEN12+ Reg State Context */
 #define GEN12_CTX_BB_PER_CTX_PTR		0x12
 #define GEN12_CTX_LRI_HEADER_3			0x41