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From: "fretre lewis" <fretre3618@hotmail.com>
To: linux-kernel@vger.kernel.org
Subject: PCI code:  why need  outb (0x01, 0xCFB); ?
Date: Mon, 06 Jan 2003 09:26:50 +0000
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  thank Alan Cox and John Bradford , very nice.

  however, I am afraid I haven't make my idea quite clear because of my pool
english, permit me saying again:

  I am learning code about pci_check_direct(), at 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 think "outb (0x01, 0xCFB);" just is a normal write to a device at port
address 0xCFB (maybe wrong, fix me), then my questions are:

1. which device is at port address 0xCFB?

2. what is meaning of the writing operation "outb (0x01, 0xCFB);" for THIS
device?, it'seem that PCI spec v2.0 not say anything about it?

3. why need "outb (0x01, 0xCFB);" before configuration operation "outl
(0x80000000, 0xCF8);" if check configuration type 1? and why need "outb
(0x00, 0xCFB);" before "outb (0x00, 0xCF8);" 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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