drm/radeon: check if device is root before getting pci speed caps

Check if the device is root rather before attempting to see what
speeds the pcie port supports.  Fixes a crash with pci passthrough
in a VM.

Bug: https://bugs.freedesktop.org/show_bug.cgi?id=109366Reviewed-by: Evan Quan <evan.quan@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>

drivers/gpu/drm/radeon/ci_dpm.c

@@ -5676,7 +5676,7 @@ int ci_dpm_init(struct radeon_device *rdev)
 	u16 data_offset, size;
 	u8 frev, crev;
 	struct ci_power_info *pi;
-	enum pci_bus_speed speed_cap;
+	enum pci_bus_speed speed_cap = PCI_SPEED_UNKNOWN;
 	struct pci_dev *root = rdev->pdev->bus->self;
 	int ret;
 
@@ -5685,7 +5685,8 @@ int ci_dpm_init(struct radeon_device *rdev)
 		return -ENOMEM;
 	rdev->pm.dpm.priv = pi;
 
-	speed_cap = pcie_get_speed_cap(root);
+	if (!pci_is_root_bus(rdev->pdev->bus))
+		speed_cap = pcie_get_speed_cap(root);
 	if (speed_cap == PCI_SPEED_UNKNOWN) {
 		pi->sys_pcie_mask = 0;
 	} else {

drivers/gpu/drm/radeon/si_dpm.c

@@ -6899,7 +6899,7 @@ int si_dpm_init(struct radeon_device *rdev)
 	struct ni_power_info *ni_pi;
 	struct si_power_info *si_pi;
 	struct atom_clock_dividers dividers;
-	enum pci_bus_speed speed_cap;
+	enum pci_bus_speed speed_cap = PCI_SPEED_UNKNOWN;
 	struct pci_dev *root = rdev->pdev->bus->self;
 	int ret;
 
@@ -6911,7 +6911,8 @@ int si_dpm_init(struct radeon_device *rdev)
 	eg_pi = &ni_pi->eg;
 	pi = &eg_pi->rv7xx;
 
-	speed_cap = pcie_get_speed_cap(root);
+	if (!pci_is_root_bus(rdev->pdev->bus))
+		speed_cap = pcie_get_speed_cap(root);
 	if (speed_cap == PCI_SPEED_UNKNOWN) {
 		si_pi->sys_pcie_mask = 0;
 	} else {