PCICAP_NEXTPTR
ptr = pci_read_config(child, ptr + PCICAP_NEXTPTR, 1);
nextptr = REG(ptr + PCICAP_NEXTPTR, 1);
ptr = read_config(fd, &p->pc_sel, ptr + PCICAP_NEXTPTR, 1);
ptr = read_config(fd, &p->pc_sel, ptr + PCICAP_NEXTPTR, 1);