drm/amdgpu: 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.  Moreover AMD's Windows driver special-cases Thunderbolt as
well.
Acked-by: NAlex Deucher <alexander.deucher@amd.com>
Signed-off-by: NLukas Wunner <lukas@wunner.de>
Link: http://patchwork.freedesktop.org/patch/msgid/701a8e89ce8ac39734736ab779558b6a4042a19e.1489145162.git.lukas@wunner.de

drivers/gpu/drm/amd/amdgpu/amdgpu_device.c

@@ -1763,7 +1763,9 @@ int amdgpu_device_init(struct amdgpu_device *adev,
 		runtime = true;
 	if (amdgpu_device_is_px(ddev))
 		runtime = true;
-	vga_switcheroo_register_client(adev->pdev, &amdgpu_switcheroo_ops, runtime);
+	if (!pci_is_thunderbolt_attached(adev->pdev))
+		vga_switcheroo_register_client(adev->pdev,
+					       &amdgpu_switcheroo_ops, runtime);
 	if (runtime)
 		vga_switcheroo_init_domain_pm_ops(adev->dev, &adev->vga_pm_domain);
 
@@ -1926,7 +1928,8 @@ void amdgpu_device_fini(struct amdgpu_device *adev)
 	amdgpu_atombios_fini(adev);
 	kfree(adev->bios);
 	adev->bios = NULL;
-	vga_switcheroo_unregister_client(adev->pdev);
+	if (!pci_is_thunderbolt_attached(adev->pdev))
+		vga_switcheroo_unregister_client(adev->pdev);
 	if (adev->flags & AMD_IS_PX)
 		vga_switcheroo_fini_domain_pm_ops(adev->dev);
 	vga_client_register(adev->pdev, NULL, NULL, NULL);

drivers/gpu/drm/amd/amdgpu/amdgpu_kms.c

@@ -103,7 +103,8 @@ int amdgpu_driver_load_kms(struct drm_device *dev, unsigned long flags)
 	    amdgpu_has_atpx() &&
 	    (amdgpu_is_atpx_hybrid() ||
 	     amdgpu_has_atpx_dgpu_power_cntl()) &&
-	    ((flags & AMD_IS_APU) == 0))
+	    ((flags & AMD_IS_APU) == 0) &&
+	    !pci_is_thunderbolt_attached(dev->pdev))
 		flags |= AMD_IS_PX;
 
 	/* amdgpu_device_init should report only fatal error