drm/nouveau: Don't register Thunderbolt eGPU with vga_switcheroo

An external Thunderbolt GPU can neither drive the laptop's panel nor be
powered off by the platform, so there's no point in registering it with
vga_switcheroo.  In fact, when the external GPU is runtime suspended,
vga_switcheroo will cut power to the internal discrete GPU, resulting in
a lockup.

Cc: Ben Skeggs <bskeggs@redhat.com>
Acked-by: Alex Deucher <alexander.deucher@amd.com>
Signed-off-by: Lukas Wunner <lukas@wunner.de>
Link: http://patchwork.freedesktop.org/patch/msgid/8e733152b13e7c14501ad5af45c1c5c736584111.1489145162.git.lukas@wunner.de

drivers/gpu/drm/nouveau/nouveau_vga.c

@@ -95,6 +95,10 @@ nouveau_vga_init(struct nouveau_drm *drm)
 
 	vga_client_register(dev->pdev, dev, NULL, nouveau_vga_set_decode);
 
+	/* don't register Thunderbolt eGPU with vga_switcheroo */
+	if (pci_is_thunderbolt_attached(dev->pdev))
+		return;
+
 	if (nouveau_runtime_pm == 1)
 		runtime = true;
 	if ((nouveau_runtime_pm == -1) && (nouveau_is_optimus() || nouveau_is_v1_dsm()))
@@ -111,6 +115,11 @@ nouveau_vga_fini(struct nouveau_drm *drm)
 	struct drm_device *dev = drm->dev;
 	bool runtime = false;
 
+	vga_client_register(dev->pdev, NULL, NULL, NULL);
+
+	if (pci_is_thunderbolt_attached(dev->pdev))
+		return;
+
 	if (nouveau_runtime_pm == 1)
 		runtime = true;
 	if ((nouveau_runtime_pm == -1) && (nouveau_is_optimus() || nouveau_is_v1_dsm()))
@@ -119,7 +128,6 @@ nouveau_vga_fini(struct nouveau_drm *drm)
 	vga_switcheroo_unregister_client(dev->pdev);
 	if (runtime && nouveau_is_v1_dsm() && !nouveau_is_optimus())
 		vga_switcheroo_fini_domain_pm_ops(drm->dev->dev);
-	vga_client_register(dev->pdev, NULL, NULL, NULL);
 }