drm/amdgpu: register a vga_switcheroo client for MacBooks with apple-gmux

Commit 3840c5bcc245 ("drm/amdgpu: disentangle runtime pm and
vga_switcheroo") made amdgpu only register a vga_switcheroo client for
GPU's with PX, however AMD GPUs in dual gpu Apple Macbooks do need to
register, but don't have PX. Instead of AMD's PX, they use apple-gmux.

Use apple_gmux_detect() to identify these gpus, and
pci_is_thunderbolt_attached() to ensure eGPUs connected to Dual GPU
Macbooks don't register with vga_switcheroo.

Fixes: 3840c5bcc245 ("drm/amdgpu: disentangle runtime pm and vga_switcheroo")
Link: https://lore.kernel.org/amd-gfx/[e-mail]/
Signed-off-by: Orlando Chamberlain <[e-mail]>
Signed-off-by: Alex Deucher <[e-mail]>

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

···
 #include <linux/devcoredump.h>
 #include <generated/utsrelease.h>
 #include <linux/pci-p2pdma.h>
+#include <linux/apple-gmux.h>
 
 #include <drm/drm_aperture.h>
 #include <drm/drm_atomic_helper.h>
···
 	if ((adev->pdev->class >> 8) == PCI_CLASS_DISPLAY_VGA)
 		vga_client_register(adev->pdev, amdgpu_device_vga_set_decode);
 
-	if (amdgpu_device_supports_px(ddev)) {
-		px = true;
+	px = amdgpu_device_supports_px(ddev);
+
+	if (px || (!pci_is_thunderbolt_attached(adev->pdev) &&
+				apple_gmux_detect(NULL, NULL)))
 		vga_switcheroo_register_client(adev->pdev,
 					       &amdgpu_switcheroo_ops, px);
+
+	if (px)
 		vga_switcheroo_init_domain_pm_ops(adev->dev, &adev->vga_pm_domain);
-	}
 
 	if (adev->gmc.xgmi.pending_reset)
 		queue_delayed_work(system_wq, &mgpu_info.delayed_reset_work,
···
 void amdgpu_device_fini_sw(struct amdgpu_device *adev)
 {
 	int idx;
+	bool px;
 
 	amdgpu_fence_driver_sw_fini(adev);
 	amdgpu_device_ip_fini(adev);
···
 
 	kfree(adev->bios);
 	adev->bios = NULL;
-	if (amdgpu_device_supports_px(adev_to_drm(adev))) {
+
+	px = amdgpu_device_supports_px(adev_to_drm(adev));
+
+	if (px || (!pci_is_thunderbolt_attached(adev->pdev) &&
+				apple_gmux_detect(NULL, NULL)))
 		vga_switcheroo_unregister_client(adev->pdev);
+
+	if (px)
 		vga_switcheroo_fini_domain_pm_ops(adev->dev);
-	}
+
 	if ((adev->pdev->class >> 8) == PCI_CLASS_DISPLAY_VGA)
 		vga_client_unregister(adev->pdev);