/* * Important note about PCI-ISA bridges: * * Callbacks are used to configure these devices so that ISA/EISA bridges * can attach their child busses after PCI configuration is done. * * This works because: * (1) there can be at most one ISA/EISA bridge per PCI bus, and * (2) any ISA/EISA bridges must be attached to primary PCI * busses (i.e. bus zero). * * That boils down to: there can only be one of these outstanding * at a time, it is cleared when configuring PCI bus 0 before any * subdevices have been found, and it is run after all subdevices * of PCI bus 0 have been found. * * This is needed because there are some (legacy) PCI devices which * can show up as ISA/EISA devices as well (the prime example of which * are VGA controllers). If you attach ISA from a PCI-ISA/EISA bridge, * and the bridge is seen before the video board is, the board can show * up as an ISA device, and that can (bogusly) complicate the PCI device's * attach code, or make the PCI device not be properly attached at all. * * We use the generic config_defer() facility to achieve this. */