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Subjectplease help me understand a line code about pci
Date

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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