cursor-renderer/native: Handle GPU hotplug

Listen for GPU hotplug events to initialize their cursor support.

This fixes one reason for why DisplayLink devices may not be using a hardware
cursor. Particularly, when a DisplayLink device is hotplugged for the first
time such that EVDI creates a new DRM device node after gnome-shell has already
started, we used to forget to initialize the cursor support.

https://gitlab.gnome.org/GNOME/mutter/merge_requests/1097
(cherry picked from commit 8abdf16a39)

src/backends/native/meta-cursor-renderer-native.c

@@ -2,6 +2,7 @@
 
 /*
  * Copyright (C) 2014 Red Hat
+ * Copyright 2020 DisplayLink (UK) Ltd.
  *
  * This program is free software; you can redistribute it and/or
  * modify it under the terms of the GNU General Public License as
@@ -1205,6 +1206,13 @@ init_hw_cursor_support_for_gpu (MetaGpuKms *gpu_kms)
     }
 }
 
+static void
+on_gpu_added_for_cursor (MetaBackend *backend,
+                         MetaGpuKms  *gpu_kms)
+{
+  init_hw_cursor_support_for_gpu (gpu_kms);
+}
+
 static void
 init_hw_cursor_support (MetaCursorRendererNative *cursor_renderer_native)
 {
@@ -1238,6 +1246,8 @@ meta_cursor_renderer_native_new (MetaBackend *backend)
   g_signal_connect_object (monitor_manager, "monitors-changed-internal",
                            G_CALLBACK (on_monitors_changed),
                            cursor_renderer_native, 0);
+  g_signal_connect (backend, "gpu-added",
+                    G_CALLBACK (on_gpu_added_for_cursor), NULL);
 
   priv->backend = backend;
   priv->hw_state_invalidated = TRUE;