drm/i915: Increase the amount of defense before computing vblank timestamps

Reported-by: NChris Clayton <chris2553@googlemail.com>
Tested-by: NChris Clayton <chris2553@googlemail.com>
Signed-off-by: NChris Wilson <chris@chris-wilson.co.uk>

drivers/gpu/drm/i915/i915_irq.c

@@ -274,24 +274,35 @@ int i915_get_crtc_scanoutpos(struct drm_device *dev, int pipe,
 	return ret;
 }
 
-int i915_get_vblank_timestamp(struct drm_device *dev, int crtc,
+int i915_get_vblank_timestamp(struct drm_device *dev, int pipe,
 			      int *max_error,
 			      struct timeval *vblank_time,
 			      unsigned flags)
 {
-	struct drm_crtc *drmcrtc;
+	struct drm_i915_private *dev_priv = dev->dev_private;
+	struct drm_crtc *crtc;
 
-	if (crtc < 0 || crtc >= dev->num_crtcs) {
-		DRM_ERROR("Invalid crtc %d\n", crtc);
+	if (pipe < 0 || pipe >= dev_priv->num_pipe) {
+		DRM_ERROR("Invalid crtc %d\n", pipe);
 		return -EINVAL;
 	}
 
 	/* Get drm_crtc to timestamp: */
-	drmcrtc = intel_get_crtc_for_pipe(dev, crtc);
+	crtc = intel_get_crtc_for_pipe(dev, pipe);
+	if (crtc == NULL) {
+		DRM_ERROR("Invalid crtc %d\n", pipe);
+		return -EINVAL;
+	}
+
+	if (!crtc->enabled) {
+		DRM_DEBUG_KMS("crtc %d is disabled\n", pipe);
+		return -EBUSY;
+	}
 
 	/* Helper routine in DRM core does all the work: */
-	return drm_calc_vbltimestamp_from_scanoutpos(dev, crtc, max_error,
-						     vblank_time, flags, drmcrtc);
+	return drm_calc_vbltimestamp_from_scanoutpos(dev, pipe, max_error,
+						     vblank_time, flags,
+						     crtc);
 }
 
 /*