+ ret = dm_pci_bus_find_bdf(TNC_SDVO, &sdvo);
+ if (ret)
+ return ret;
+ if (!sdvo)
+ return 0;
+
+ /*
+ * According to Atom E6xx datasheet, setting VGA Disable (bit17)
+ * of Graphics Controller register (offset 0x50) prevents IGD
+ * (D2:F0) from reporting itself as a VGA display controller
+ * class in the PCI configuration space, and should also prevent
+ * it from responding to VGA legacy memory range and I/O addresses.
+ *
+ * However test result shows that with just VGA Disable bit set and
+ * a PCIe graphics card connected to one of the PCIe controllers on
+ * the E6xx, accessing the VGA legacy space still causes system hang.
+ * After a number of attempts, it turns out besides VGA Disable bit,
+ * the SDVO (D3:F0) device should be disabled to make it work.
+ *
+ * To simplify, use the Function Disable register (offset 0xc4)
+ * to disable both IGD (D2:F0) and SDVO (D3:F0) devices. Now these
+ * two devices will be completely disabled (invisible in the PCI
+ * configuration space) unless a system reset is performed.
+ */
+ dm_pci_write_config32(igd, IGD_FD, FUNC_DISABLE);
+ dm_pci_write_config32(sdvo, IGD_FD, FUNC_DISABLE);
+
+ /*
+ * After setting the function disable bit, IGD and SDVO devices will
+ * disappear in the PCI configuration space. This however creates an
+ * inconsistent state from a driver model PCI controller point of view,
+ * as these two PCI devices are still attached to its parent's child
+ * device list as maintained by the driver model. Some driver model PCI
+ * APIs like dm_pci_find_class(), are referring to the list to speed up
+ * the finding process instead of re-enumerating the whole PCI bus, so
+ * it gets the stale cached data which is wrong.
+ *
+ * Note x86 PCI enueration normally happens twice, in pre-relocation
+ * phase and post-relocation. One option might be to call disable_igd()
+ * in one of the pre-relocation initialization hooks so that it gets
+ * disabled in the first round, and when it comes to the second round
+ * driver model PCI will construct a correct list. Unfortunately this
+ * does not work as Intel FSP is used on this platform to perform low
+ * level initialization, and fsp_init_phase_pci() is called only once
+ * in the post-relocation phase. If we disable IGD and SDVO devices,
+ * fsp_init_phase_pci() simply hangs and never returns.
+ *
+ * So the only option we have is to manually remove these two devices.
+ */
+ ret = device_remove(igd);
+ if (ret)
+ return ret;
+ ret = device_unbind(igd);
+ if (ret)
+ return ret;
+ ret = device_remove(sdvo);
+ if (ret)
+ return ret;
+ ret = device_unbind(sdvo);
+ if (ret)
+ return ret;