drm/i915: Reset state after a GPU reset or resume

Call drm_mode_config_reset() after an invalidation event to restore any
cached state to unknown.
Tested-by: NTakashi Iwai <tiwai@suse.de>
Signed-off-by: NChris Wilson <chris@chris-wilson.co.uk>

drivers/gpu/drm/i915/i915_drv.c

@@ -354,6 +354,7 @@ static int i915_drm_thaw(struct drm_device *dev)
 		error = i915_gem_init_ringbuffer(dev);
 		mutex_unlock(&dev->struct_mutex);
 
+		drm_mode_config_reset(dev);
 		drm_irq_install(dev);
 
 		/* Resume the modeset for every activated CRTC */
@@ -542,6 +543,7 @@ int i915_reset(struct drm_device *dev, u8 flags)
 
 		mutex_unlock(&dev->struct_mutex);
 		drm_irq_uninstall(dev);
+		drm_mode_config_reset(dev);
 		drm_irq_install(dev);
 		mutex_lock(&dev->struct_mutex);
 	}