drm/i915: hangcheck disable parameter

Provide a parameter to disable hanghcheck. This is useful mostly for
developers trying to debug known problems, and probably should not be
touched by normal users.

Reviewed-by: Chris Wilson <chris@chris-wilson.co.uk>
Signed-off-by: Ben Widawsky <ben@bwidawsk.net>
Signed-off-by: Keith Packard <keithp@keithp.com>

drivers/gpu/drm/i915/i915_drv.c

@@ -70,6 +70,9 @@ module_param_named(vbt_sdvo_panel_type, i915_vbt_sdvo_panel_type, int, 0600);
 static bool i915_try_reset = true;
 module_param_named(reset, i915_try_reset, bool, 0600);
 
+bool i915_enable_hangcheck = true;
+module_param_named(enable_hangcheck, i915_enable_hangcheck, bool, 0644);
+
 static struct drm_driver driver;
 extern int intel_agp_enabled;
 

drivers/gpu/drm/i915/i915_drv.h

@@ -994,6 +994,7 @@ extern unsigned int i915_panel_use_ssc;
 extern int i915_vbt_sdvo_panel_type;
 extern unsigned int i915_enable_rc6;
 extern unsigned int i915_enable_fbc;
+extern bool i915_enable_hangcheck;
 
 extern int i915_suspend(struct drm_device *dev, pm_message_t state);
 extern int i915_resume(struct drm_device *dev);

drivers/gpu/drm/i915/i915_gem.c

@@ -1779,8 +1779,11 @@ i915_add_request(struct intel_ring_buffer *ring,
 	ring->outstanding_lazy_request = false;
 
 	if (!dev_priv->mm.suspended) {
-		mod_timer(&dev_priv->hangcheck_timer,
-			  jiffies + msecs_to_jiffies(DRM_I915_HANGCHECK_PERIOD));
+		if (i915_enable_hangcheck) {
+			mod_timer(&dev_priv->hangcheck_timer,
+				  jiffies +
+				  msecs_to_jiffies(DRM_I915_HANGCHECK_PERIOD));
+		}
 		if (was_empty)
 			queue_delayed_work(dev_priv->wq,
 					   &dev_priv->mm.retire_work, HZ);

drivers/gpu/drm/i915/i915_irq.c

@@ -361,10 +361,12 @@ static void notify_ring(struct drm_device *dev,
 
 	ring->irq_seqno = seqno;
 	wake_up_all(&ring->irq_queue);
-
-	dev_priv->hangcheck_count = 0;
-	mod_timer(&dev_priv->hangcheck_timer,
-		  jiffies + msecs_to_jiffies(DRM_I915_HANGCHECK_PERIOD));
+	if (i915_enable_hangcheck) {
+		dev_priv->hangcheck_count = 0;
+		mod_timer(&dev_priv->hangcheck_timer,
+			  jiffies +
+			  msecs_to_jiffies(DRM_I915_HANGCHECK_PERIOD));
+	}
 }
 
 static void gen6_pm_rps_work(struct work_struct *work)
@@ -1664,6 +1666,9 @@ void i915_hangcheck_elapsed(unsigned long data)
 	uint32_t acthd, instdone, instdone1;
 	bool err = false;
 
+	if (!i915_enable_hangcheck)
+		return;
+
 	/* If all work is done then ACTHD clearly hasn't advanced. */
 	if (i915_hangcheck_ring_idle(&dev_priv->ring[RCS], &err) &&
 	    i915_hangcheck_ring_idle(&dev_priv->ring[VCS], &err) &&