pcibios_write_config_byte
pcibios_write_config_byte(p->bus, p->devfn, PCI_LATENCY_TIMER, 32);
extern int pcibios_write_config_byte (unsigned int bus, unsigned int device_fn, unsigned int where, uint8_t value);
return pcibios_write_config_byte(dev->bus, dev->devfn, where, value);
pcibios_write_config_byte(p->bus,p->devfn, 0x48, reg | 0x40);
pcibios_write_config_byte(p->bus,p->devfn, 0x48, reg & ~0x40);