please help me understand a line code about pci

From: fretre lewis (fretre3618@hotmail.com)
Date: Sat Jan 04 2003 - 06:59:11 EST


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

the PCI spec v2.0 say: ( page32)

"Anytime a host bridge sees a full DWORD I/O write from the host to
CONFIG_ADDRESS, the bridge must latch the data into its CONFIG_ADDRESS
register. On full DWORD I/O reads to CONFIG_ADDRESS,the bridge must return
the
data in CONFIG_ADDRESS. Any other types of accesses to this
address(non-DWORD)
have no effect on CONFIG_ADDRESS and are excuted as normal I/O transaction
on PCI bus......"

CONFIG_ADDRESS = 0xcf8
CONFIG_data = 0xcfc

so , 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

_________________________________________________________________
Help STOP SPAM: Try the new MSN 8 and get 2 months FREE*
http://join.msn.com/?page=features/junkmail

-
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to majordomo@vger.kernel.org
More majordomo info at http://vger.kernel.org/majordomo-info.html
Please read the FAQ at http://www.tux.org/lkml/



This archive was generated by hypermail 2b29 : Tue Jan 07 2003 - 22:00:25 EST