please help me understand a line code about pci

["fretre lewis" <fretre3618@hotmail.com>]

hi,all

  I am reading code about pci, and I can't understand some lines in
pci_check_direct(), in arch/i386/kernel/pci-pc.c

well, I wonder why need "outb (0x01, 0xCFB);" if check configuration type 1 
? and why "outb (0x00, 0xCFB);" if check configuration type 2?
  please help me,thanks a lot.


406 static struct pci_ops * __devinit pci_check_direct(void)
407 {
408         unsigned int tmp;
409         unsigned long flags;
410
411         __save_flags(flags); __cli();
412
413         /*
414          * Check if configuration type 1 works.
415          */
416         if (pci_probe & PCI_PROBE_CONF1) {
417                 outb (0x01, 0xCFB);  <<<=========
418                 tmp = inl (0xCF8);
419                 outl (0x80000000, 0xCF8);
420                 if (inl (0xCF8) == 0x80000000 &&
421                     pci_sanity_check(&pci_direct_conf1)) {
422                         outl (tmp, 0xCF8);
423                         __restore_flags(flags);
424                         printk(KERN_INFO "PCI: Using configuration type 
1\n");
425                         request_region(0xCF8, 8, "PCI conf1");
426                         return &pci_direct_conf1;
427                 }
428                 outl (tmp, 0xCF8);
429         }
430
431         /*
432          * Check if configuration type 2 works.
433          */
434         if (pci_probe & PCI_PROBE_CONF2) {
435                 outb (0x00, 0xCFB);   <<<=========
436                 outb (0x00, 0xCF8);
437                 outb (0x00, 0xCFA);
438                 if (inb (0xCF8) == 0x00 && inb (0xCFA) == 0x00 &&
439                     pci_sanity_check(&pci_direct_conf2)) {
440                         __restore_flags(flags);
441                         printk(KERN_INFO "PCI: Using configuration type 
2\n");
442                         request_region(0xCF8, 4, "PCI conf2");
443                         return &pci_direct_conf2;
444                 }
445         }
446
447         __restore_flags(flags);
448         return NULL;
449 }
450
451 #endif





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