drm/fb-helper: Improve error reporting in setup

Improve error reporting in drm_fb_helper_fbdev_setup() by printing the
error code. This is useful for drivers that choose to not fall over just
because fbdev doesen't work, but still wants clues to why it failed.
This way they don't have to provide an error message themselves.
Signed-off-by: Noralf Trønnes <noralf@tronnes.org>
Acked-by: Sam Ravnborg <sam@ravnborg.org>
Link: https://patchwork.freedesktop.org/patch/msgid/20180908134648.2582-2-noralf@tronnes.org

drivers/gpu/drm/drm_fb_helper.c

@@ -2846,7 +2846,7 @@ int drm_fb_helper_fbdev_setup(struct drm_device *dev,
 	if (!max_conn_count)
 		max_conn_count = dev->mode_config.num_connector;
 	if (!max_conn_count) {
-		DRM_DEV_ERROR(dev->dev, "No connectors\n");
+		DRM_DEV_ERROR(dev->dev, "fbdev: No connectors\n");
 		return -EINVAL;
 	}
 
@@ -2854,13 +2854,13 @@ int drm_fb_helper_fbdev_setup(struct drm_device *dev,
 
 	ret = drm_fb_helper_init(dev, fb_helper, max_conn_count);
 	if (ret < 0) {
-		DRM_DEV_ERROR(dev->dev, "Failed to initialize fbdev helper\n");
+		DRM_DEV_ERROR(dev->dev, "fbdev: Failed to initialize (ret=%d)\n", ret);
 		return ret;
 	}
 
 	ret = drm_fb_helper_single_add_all_connectors(fb_helper);
 	if (ret < 0) {
-		DRM_DEV_ERROR(dev->dev, "Failed to add connectors\n");
+		DRM_DEV_ERROR(dev->dev, "fbdev: Failed to add connectors (ret=%d)\n", ret);
 		goto err_drm_fb_helper_fini;
 	}
 
@@ -2869,7 +2869,7 @@ int drm_fb_helper_fbdev_setup(struct drm_device *dev,
 
 	ret = drm_fb_helper_initial_config(fb_helper, preferred_bpp);
 	if (ret < 0) {
-		DRM_DEV_ERROR(dev->dev, "Failed to set fbdev configuration\n");
+		DRM_DEV_ERROR(dev->dev, "fbdev: Failed to set configuration (ret=%d)\n", ret);
 		goto err_drm_fb_helper_fini;
 	}