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
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> 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?
It looks to me like a workaround for broken hardware, but I could be
wrong.
Incidently, wouldn't it be worth printing some debugging info, such as
the values read from 0xCF8 and 0xCFA, when neither configuration type
works? I've attached an, (untested), patch to do so.
John.
On Sat, 2003-01-04 at 12:14, John Bradford wrote:
> Incidently, wouldn't it be worth printing some debugging info, such as
> the values read from 0xCF8 and 0xCFA, when neither configuration type
> works? I've attached an, (untested), patch to do so.
That just indicates a system using a non standard conf type - thats
perfectly reasonable.