drm/fb-helper: Restore damage area upon errors

If the damage handling fails, restore the damage area. The next invocation
of the damage worker will then perform the update.

v3:
	* Use drm_WARN_ONCE() with an error message to print warning
v2:
	* print a single warning if dirty callback fails (Daniel, Sebastian)
	* update comment
Signed-off-by: Thomas Zimmermann <tzimmermann@suse.de>
Acked-by: Maxime Ripard <mripard@kernel.org>
Acked-by: Sam Ravnborg <sam@ravnborg.org>
Link: https://patchwork.freedesktop.org/patch/msgid/20201120102545.4047-9-tzimmermann@suse.de

drivers/gpu/drm/drm_fb_helper.c

@@ -432,11 +432,28 @@ static void drm_fb_helper_damage_work(struct work_struct *work)
 	if (helper->buffer) {
 		ret = drm_fb_helper_damage_blit(helper, &clip_copy);
 		if (drm_WARN_ONCE(dev, ret, "Damage blitter failed: ret=%d\n", ret))
-			return;
+			goto err;
+	}
+
+	if (helper->fb->funcs->dirty) {
+		ret = helper->fb->funcs->dirty(helper->fb, NULL, 0, 0, &clip_copy, 1);
+		if (drm_WARN_ONCE(dev, ret, "Dirty helper failed: ret=%d\n", ret))
+			goto err;
 	}
 
-	if (helper->fb->funcs->dirty)
-		helper->fb->funcs->dirty(helper->fb, NULL, 0, 0, &clip_copy, 1);
+	return;
+
+err:
+	/*
+	 * Restore damage clip rectangle on errors. The next run
+	 * of the damage worker will perform the update.
+	 */
+	spin_lock_irqsave(&helper->damage_lock, flags);
+	clip->x1 = min_t(u32, clip->x1, clip_copy.x1);
+	clip->y1 = min_t(u32, clip->y1, clip_copy.y1);
+	clip->x2 = max_t(u32, clip->x2, clip_copy.x2);
+	clip->y2 = max_t(u32, clip->y2, clip_copy.y2);
+	spin_unlock_irqrestore(&helper->damage_lock, flags);
 }
 
 /**