drm/amdgpu: check before checking pci bridge registers

commit e79d5c08 upstream.

Make sure we are not the root device before attempting to
read the pcie bridge registers to check the pcie gen speeed.

Fixes a crash when the device is passed through to a VM.
Reviewed-by: Christian König <christian.koenig@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

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

@@ -1565,6 +1565,9 @@ static void cik_pcie_gen3_enable(struct amdgpu_device *adev)
 	int ret, i;
 	u16 tmp16;
 
+	if (pci_is_root_bus(adev->pdev->bus))
+		return;
+
 	if (amdgpu_pcie_gen2 == 0)
 		return;
 

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

@@ -968,6 +968,9 @@ static void vi_pcie_gen3_enable(struct amdgpu_device *adev)
 	u32 mask;
 	int ret;
 
+	if (pci_is_root_bus(adev->pdev->bus))
+		return;
+
 	if (amdgpu_pcie_gen2 == 0)
 		return;