pci_check_type2() help.

[Onkar N Mahajan <kernzap@gmail.com>]

Hello list, 

I am trying to understand the PCI functionality in Linux kernel. 
What is the best way to start to understanding this - where to start 
in the kernel code ? Books ? Manuals ? 

I started reading the code - where I am stuck in this function -
pci_check_type2() ; Wherein I am not able to get from where these values
0xCFB,0xCF8,0xCFA are arrived at ? I guess these are port numbers , but 
in which manuals can I find this all information. 

linux/arch/x86/pci/init.c: 
static int __init pci_check_type2(void)
{
    unsigned long flags;
    int works = 0;

    local_irq_save(flags);

    outb(0x00, 0xCFB);
    outb(0x00, 0xCF8);
    outb(0x00, 0xCFA);
    if (inb(0xCF8) == 0x00 && inb(0xCFA) == 0x00 &&
        pci_sanity_check(&pci_direct_conf2)) {
        works = 1;
    }

    local_irq_restore(flags);

    return works;
}


Please help me figuring out right manuals for this. 


-- Onkar