drm/pci: add support for getting the supported link bw.

This should work for PCIE3.0 as well.
Signed-off-by: Dave Airlie <airlied@redhat.com>

drivers/gpu/drm/drm_pci.c

@@ -465,3 +465,52 @@ void drm_pci_exit(struct drm_driver *driver, struct pci_driver *pdriver)
 	DRM_INFO("Module unloaded\n");
 }
 EXPORT_SYMBOL(drm_pci_exit);
+
+int drm_pcie_get_speed_cap_mask(struct drm_device *dev, u32 *mask)
+{
+	struct pci_dev *root;
+	int pos;
+	u32 lnkcap, lnkcap2;
+
+	*mask = 0;
+	if (!dev->pdev)
+		return -EINVAL;
+
+	if (!pci_is_pcie(dev->pdev))
+		return -EINVAL;
+
+	root = dev->pdev->bus->self;
+
+	pos = pci_pcie_cap(root);
+	if (!pos)
+		return -EINVAL;
+
+	/* we've been informed via and serverworks don't make the cut */
+	if (root->vendor == PCI_VENDOR_ID_VIA ||
+	    root->vendor == PCI_VENDOR_ID_SERVERWORKS)
+		return -EINVAL;
+
+	pci_read_config_dword(root, pos + PCI_EXP_LNKCAP, &lnkcap);
+	pci_read_config_dword(root, pos + PCI_EXP_LNKCAP2, &lnkcap2);
+
+	lnkcap &= PCI_EXP_LNKCAP_SLS;
+	lnkcap2 &= 0xfe;
+
+	if (lnkcap2) { /* PCIE GEN 3.0 */
+		if (lnkcap2 & PCI_EXP_LNKCAP2_SLS_2_5GB)
+			*mask |= DRM_PCIE_SPEED_25;
+		if (lnkcap2 & PCI_EXP_LNKCAP2_SLS_5_0GB)
+			*mask |= DRM_PCIE_SPEED_50;
+		if (lnkcap2 & PCI_EXP_LNKCAP2_SLS_8_0GB)
+			*mask |= DRM_PCIE_SPEED_80;
+	} else {
+		if (lnkcap & 1)
+			*mask |= DRM_PCIE_SPEED_25;
+		if (lnkcap & 2)
+			*mask |= DRM_PCIE_SPEED_50;
+	}
+
+	DRM_INFO("probing gen 2 caps for device %x:%x = %x/%x\n", root->vendor, root->device, lnkcap, lnkcap2);
+	return 0;
+}
+EXPORT_SYMBOL(drm_pcie_get_speed_cap_mask);

include/drm/drmP.h

@@ -1761,6 +1761,11 @@ extern int drm_get_pci_dev(struct pci_dev *pdev,
 			   const struct pci_device_id *ent,
 			   struct drm_driver *driver);
 
+#define DRM_PCIE_SPEED_25 1
+#define DRM_PCIE_SPEED_50 2
+#define DRM_PCIE_SPEED_80 4
+
+extern int drm_pcie_get_speed_cap_mask(struct drm_device *dev, u32 *speed_mask);
 
 /* platform section */
 extern int drm_platform_init(struct drm_driver *driver, struct platform_device *platform_device);