diff --git a/drivers/gpu/drm/drm_plane.c b/drivers/gpu/drm/drm_plane.c
index e40c12fabbde..d3b92eaa481c 100644
--- a/drivers/gpu/drm/drm_plane.c
+++ b/drivers/gpu/drm/drm_plane.c
@@ -806,23 +806,34 @@ int drm_mode_page_flip_ioctl(struct drm_device *dev,
 	struct drm_modeset_acquire_ctx ctx;
 	int ret = -EINVAL;
 
-	if (!drm_core_check_feature(dev, DRIVER_MODESET))
+	if (!drm_core_check_feature(dev, DRIVER_MODESET)) {
+		DRM_WARN_ONCE("DRIVER_MODESET feature not enabled\n");
 		return -EINVAL;
+	}
 
-	if (page_flip->flags & ~DRM_MODE_PAGE_FLIP_FLAGS)
+	if (page_flip->flags & ~DRM_MODE_PAGE_FLIP_FLAGS) {
+		DRM_WARN_ONCE("Invalid page flip flags 0x%x\n",
+			      page_flip->flags & ~DRM_MODE_PAGE_FLIP_FLAGS);
 		return -EINVAL;
+	}
 
-	if (page_flip->sequence != 0 && !(page_flip->flags & DRM_MODE_PAGE_FLIP_TARGET))
+	if (page_flip->sequence != 0 && !(page_flip->flags & DRM_MODE_PAGE_FLIP_TARGET)) {
+		DRM_WARN_ONCE("page_flip->sequence=%u != 0, but DRM_MODE_PAGE_FLIP_TARGET flag set\n");
 		return -EINVAL;
+	}
 
 	/* Only one of the DRM_MODE_PAGE_FLIP_TARGET_ABSOLUTE/RELATIVE flags
 	 * can be specified
 	 */
-	if ((page_flip->flags & DRM_MODE_PAGE_FLIP_TARGET) == DRM_MODE_PAGE_FLIP_TARGET)
+	if ((page_flip->flags & DRM_MODE_PAGE_FLIP_TARGET) == DRM_MODE_PAGE_FLIP_TARGET) {
+		DRM_WARN_ONCE("Both DRM_MODE_PAGE_FLIP_TARGET flags set\n");
 		return -EINVAL;
+	}
 
-	if ((page_flip->flags & DRM_MODE_PAGE_FLIP_ASYNC) && !dev->mode_config.async_page_flip)
+	if ((page_flip->flags & DRM_MODE_PAGE_FLIP_ASYNC) && !dev->mode_config.async_page_flip) {
+		DRM_WARN_ONCE("DRM_MODE_PAGE_FLIP_ASYNC set, but not supported\n");
 		return -EINVAL;
+	}
 
 	crtc = drm_crtc_find(dev, page_flip->crtc_id);
 	if (!crtc)
@@ -833,15 +844,18 @@ int drm_mode_page_flip_ioctl(struct drm_device *dev,
 		int r;
 
 		r = drm_crtc_vblank_get(crtc);
-		if (r)
+		if (r) {
+			if (r == -EINVAL)
+				DRM_WARN_ONCE("drm_crtc_vblank_get returned -EINVAL\n");
 			return r;
+		}
 
 		current_vblank = drm_crtc_vblank_count(crtc);
 
 		switch (page_flip->flags & DRM_MODE_PAGE_FLIP_TARGET) {
 		case DRM_MODE_PAGE_FLIP_TARGET_ABSOLUTE:
 			if ((int)(target_vblank - current_vblank) > 1) {
-				DRM_DEBUG("Invalid absolute flip target %u, "
+				DRM_WARN_ONCE("Invalid absolute flip target %u, "
 					  "must be <= %u\n", target_vblank,
 					  current_vblank + 1);
 				drm_crtc_vblank_put(crtc);
@@ -850,7 +864,7 @@ int drm_mode_page_flip_ioctl(struct drm_device *dev,
 			break;
 		case DRM_MODE_PAGE_FLIP_TARGET_RELATIVE:
 			if (target_vblank != 0 && target_vblank != 1) {
-				DRM_DEBUG("Invalid relative flip target %u, "
+				DRM_WARN_ONCE("Invalid relative flip target %u, "
 					  "must be 0 or 1\n", target_vblank);
 				drm_crtc_vblank_put(crtc);
 				return -EINVAL;
@@ -864,18 +878,27 @@ int drm_mode_page_flip_ioctl(struct drm_device *dev,
 		}
 	} else if (crtc->funcs->page_flip == NULL ||
 		   (page_flip->flags & DRM_MODE_PAGE_FLIP_TARGET)) {
+		if (!crtc->funcs->page_flip)
+			DRM_WARN_ONCE("Neither page_flip_target nor page_flip hook set\n");
+		else
+			DRM_WARN_ONCE("DRM_MODE_PAGE_FLIP_TARGET set, but page_flip_target hook not\n");
 		return -EINVAL;
 	}
 
 	drm_modeset_acquire_init(&ctx, 0);
 retry:
 	ret = drm_modeset_lock(&crtc->mutex, &ctx);
-	if (ret)
+	if (ret) {
+		if (ret == -EINVAL)
+			DRM_WARN_ONCE("drm_modeset_lock returned -EINVAL for crtc->mutex\n");
 		goto out;
+	}
 	ret = drm_modeset_lock(&crtc->primary->mutex, &ctx);
-	if (ret)
+	if (ret) {
+		if (ret == -EINVAL)
+			DRM_WARN_ONCE("drm_modeset_lock returned -EINVAL for crtc->primary->mutex\n");
 		goto out;
-
+	}
 	if (crtc->primary->fb == NULL) {
 		/* The framebuffer is currently unbound, presumably
 		 * due to a hotplug event, that userspace has not
@@ -902,11 +925,15 @@ int drm_mode_page_flip_ioctl(struct drm_device *dev,
 	} else {
 		ret = drm_crtc_check_viewport(crtc, crtc->x, crtc->y, &crtc->mode, fb);
 	}
-	if (ret)
+	if (ret) {
+		if (ret == -EINVAL) {
+			DRM_WARN_ONCE("%s returned -EINVAL\n", crtc->state ?
+				      "drm_framebuffer_check_src_coords" : "drm_crtc_check_viewport");
 		goto out;
+	}
 
 	if (crtc->primary->fb->format != fb->format) {
-		DRM_DEBUG_KMS("Page flip is not allowed to change frame buffer format.\n");
+		DRM_WARN_ONCE("Page flip is not allowed to change frame buffer format.\n");
 		ret = -EINVAL;
 		goto out;
 	}
@@ -924,6 +951,8 @@ int drm_mode_page_flip_ioctl(struct drm_device *dev,
 		if (ret) {
 			kfree(e);
 			e = NULL;
+			if (ret == -EINVAL)
+				DRM_WARN_ONCE("drm_event_reserve_init returned -EINVAL\n");
 			goto out;
 		}
 	}
@@ -942,6 +971,8 @@ int drm_mode_page_flip_ioctl(struct drm_device *dev,
 			drm_event_cancel_free(dev, &e->base);
 		/* Keep the old fb, don't unref it. */
 		crtc->primary->old_fb = NULL;
+		if (ret == -EINVAL)
+			DRM_WARN_ONCE("page_flip(_target) hook returned -EINVAL\n");
 	} else {
 		crtc->primary->fb = fb;
 		/* Unref only the old framebuffer. */
diff --git a/drivers/gpu/drm/drm_vblank.c b/drivers/gpu/drm/drm_vblank.c
index e9f33cd805dd..34a68f757bcf 100644
--- a/drivers/gpu/drm/drm_vblank.c
+++ b/drivers/gpu/drm/drm_vblank.c
@@ -1441,11 +1441,15 @@ int drm_wait_vblank(struct drm_device *dev, void *data,
 	int ret;
 	unsigned int flags, seq, pipe, high_pipe;
 
-	if (!dev->irq_enabled)
+	if (!dev->irq_enabled) {
+		DRM_WARN_ONCE("IRQs not enabled\n");
 		return -EINVAL;
+	}
 
-	if (vblwait->request.type & _DRM_VBLANK_SIGNAL)
+	if (vblwait->request.type & _DRM_VBLANK_SIGNAL) {
+		DRM_WARN_ONCE("DRM_VBLANK_SIGNAL set\n");
 		return -EINVAL;
+	}
 
 	if (vblwait->request.type &
 	    ~(_DRM_VBLANK_TYPES_MASK | _DRM_VBLANK_FLAGS_MASK |
@@ -1463,8 +1467,11 @@ int drm_wait_vblank(struct drm_device *dev, void *data,
 		pipe = high_pipe >> _DRM_VBLANK_HIGH_CRTC_SHIFT;
 	else
 		pipe = flags & _DRM_VBLANK_SECONDARY ? 1 : 0;
-	if (pipe >= dev->num_crtcs)
+	if (pipe >= dev->num_crtcs) {
+		DRM_WARN_ONCE("pipe == %u >= dev->num_crtcs == %u\n",
+			      pipe, dev->num_crtcs);
 		return -EINVAL;
+	}
 
 	vblank = &dev->vblank[pipe];
 
@@ -1485,7 +1492,8 @@ int drm_wait_vblank(struct drm_device *dev, void *data,
 
 	ret = drm_vblank_get(dev, pipe);
 	if (ret) {
-		DRM_DEBUG("crtc %d failed to acquire vblank counter, %d\n", pipe, ret);
+		if (ret == -EINVAL)
+			DRM_WARN_ONCE("crtc %d failed to acquire vblank counter, %d\n", pipe, ret);
 		return ret;
 	}
 	seq = drm_vblank_count(dev, pipe);
@@ -1497,6 +1505,7 @@ int drm_wait_vblank(struct drm_device *dev, void *data,
 	case _DRM_VBLANK_ABSOLUTE:
 		break;
 	default:
+		DRM_WARN_ONCE("Neither DRM_VBLANK_RELATIVE nor _ABSOLUTE set\n");
 		ret = -EINVAL;
 		goto done;
 	}
@@ -1509,7 +1518,10 @@ int drm_wait_vblank(struct drm_device *dev, void *data,
 		/* must hold on to the vblank ref until the event fires
 		 * drm_vblank_put will be called asynchronously
 		 */
-		return drm_queue_vblank_event(dev, pipe, vblwait, file_priv);
+		ret = drm_queue_vblank_event(dev, pipe, vblwait, file_priv);
+		if (ret == -EINVAL)
+			DRM_WARN_ONCE("drm_queue_vblank_event returned -EINVAL\n");
+		return ret;
 	}
 
 	if (vblwait->request.sequence != seq) {