drm: add drm_pcie_get_max_link_width helper (v2)

Add a helper to get the max link width of the port.
Similar to the helper to get the max link speed.

v2: fix typo in commit message

Reviewed-by: Jammy Zhou <Jammy.Zhou@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>

1 files changed, 20 insertions, 0 deletions

diff --git a/drivers/gpu/drm/drm_pci.c b/drivers/gpu/drm/drm_pci.c
index fcd2a86acd2c..a1fff1179a97 100644
--- a/drivers/gpu/drm/drm_pci.c
+++ b/drivers/gpu/drm/drm_pci.c
@@ -410,6 +410,26 @@ int drm_pcie_get_speed_cap_mask(struct drm_device *dev, u32 *mask)
 }
 EXPORT_SYMBOL(drm_pcie_get_speed_cap_mask);
 
+int drm_pcie_get_max_link_width(struct drm_device *dev, u32 *mlw)
+{
+        struct pci_dev *root;
+        u32 lnkcap;
+
+        *mlw = 0;
+        if (!dev->pdev)
+                return -EINVAL;
+
+        root = dev->pdev->bus->self;
+
+        pcie_capability_read_dword(root, PCI_EXP_LNKCAP, &lnkcap);
+
+        *mlw = (lnkcap & PCI_EXP_LNKCAP_MLW) >> 4;
+
+        DRM_INFO("probing mlw for device %x:%x = %x\n", root->vendor, root->device, lnkcap);
+        return 0;
+}
+EXPORT_SYMBOL(drm_pcie_get_max_link_width);
+
 #else
 
 int drm_pci_init(struct drm_driver *driver, struct pci_driver *pdriver)