+
+/* On Tylersburg chipsets, some BIOSes have been known to enable the
+ ISOCH DMAR unit for the Azalia sound device, but not give it any
+ TLB entries, which causes it to deadlock. Check for that. We do
+ this in a function called from init_dmars(), instead of in a PCI
+ quirk, because we don't want to print the obnoxious "BIOS broken"
+ message if VT-d is actually disabled.
+*/
+static void __init check_tylersburg_isoch(void)
+{
+ struct pci_dev *pdev;
+ uint32_t vtisochctrl;
+
+ /* If there's no Azalia in the system anyway, forget it. */
+ pdev = pci_get_device(PCI_VENDOR_ID_INTEL, 0x3a3e, NULL);
+ if (!pdev)
+ return;
+ pci_dev_put(pdev);
+
+ /* System Management Registers. Might be hidden, in which case
+ we can't do the sanity check. But that's OK, because the
+ known-broken BIOSes _don't_ actually hide it, so far. */
+ pdev = pci_get_device(PCI_VENDOR_ID_INTEL, 0x342e, NULL);
+ if (!pdev)
+ return;
+
+ if (pci_read_config_dword(pdev, 0x188, &vtisochctrl)) {
+ pci_dev_put(pdev);
+ return;
+ }
+
+ pci_dev_put(pdev);
+
+ /* If Azalia DMA is routed to the non-isoch DMAR unit, fine. */
+ if (vtisochctrl & 1)
+ return;
+
+ /* Drop all bits other than the number of TLB entries */
+ vtisochctrl &= 0x1c;
+
+ /* If we have the recommended number of TLB entries (16), fine. */
+ if (vtisochctrl == 0x10)
+ return;
+
+ /* Zero TLB entries? You get to ride the short bus to school. */
+ if (!vtisochctrl) {
+ WARN(1, "Your BIOS is broken; DMA routed to ISOCH DMAR unit but no TLB space.\n"
+ "BIOS vendor: %s; Ver: %s; Product Version: %s\n",
+ dmi_get_system_info(DMI_BIOS_VENDOR),
+ dmi_get_system_info(DMI_BIOS_VERSION),
+ dmi_get_system_info(DMI_PRODUCT_VERSION));
+ iommu_identity_mapping |= IDENTMAP_AZALIA;
+ return;
+ }
+
+ printk(KERN_WARNING "DMAR: Recommended TLB entries for ISOCH unit is 16; your BIOS set %d\n",
+ vtisochctrl);
+}