drm/fb-helper: generic: Call drm_client_add() after setup is done

Hotplug can happen while drm_fbdev_generic_setup() is running so move
drm_client_add() call after setup is done to avoid
drm_fbdev_client_hotplug() running in two threads at the same time.

Fixes: 9060d7f4 ("drm/fb-helper: Finish the generic fbdev emulation")
Cc: stable@vger.kernel.org
Reported-by: Daniel Vetter <daniel.vetter@ffwll.ch>
Signed-off-by: Noralf Trønnes <noralf@tronnes.org>
Reviewed-by: Daniel Vetter <daniel.vetter@ffwll.ch>
Link: https://patchwork.freedesktop.org/patch/msgid/20190401141358.25309-1-noralf@tronnes.org

drivers/gpu/drm/drm_fb_helper.c

@@ -3312,8 +3312,6 @@ int drm_fbdev_generic_setup(struct drm_device *dev, unsigned int preferred_bpp)
 		return ret;
 	}
 
-	drm_client_add(&fb_helper->client);
-
 	if (!preferred_bpp)
 		preferred_bpp = dev->mode_config.preferred_depth;
 	if (!preferred_bpp)
@@ -3324,6 +3322,8 @@ int drm_fbdev_generic_setup(struct drm_device *dev, unsigned int preferred_bpp)
 	if (ret)
 		DRM_DEV_DEBUG(dev->dev, "client hotplug ret=%d\n", ret);
 
+	drm_client_add(&fb_helper->client);
+
 	return 0;
 }
 EXPORT_SYMBOL(drm_fbdev_generic_setup);