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Date: Wed, 19 Sep 2001 12:39:09 -0700
From: Jun Sun <jsun@mvista.com>
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To: Zhang Fuxin <fxzhang@ict.ac.cn>
CC: "linux-mips@oss.sgi.com" <linux-mips@oss.sgi.com>
Subject: Re: 8259 spurious interrupt (IRQ1,IRQ7,IRQ12..)
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Zhang Fuxin wrote:
> 
>  My irq dispatching code is very simple,it just read the IRR,count the first
> irq number and call do_IRQ.
>   /*
>  * the first level int-handler will jump here if it is a 8259A irq
>  */
> asmlinkage void i8259A_irqdispatch(struct pt_regs *regs)
> {
>         int isr, irq;
> 
>         isr = inb(0x20);
> 
>         irq = ffz (~isr);
> 
>         if (irq == 2) {
>                 isr = inb(0xa0);
>                 irq = 8 + ffz(~isr);
>         }
> 
>         do_IRQ(irq,regs);
> }
> 

OK, so the problem is not what I was thinking.

I don't have much clue here.  I remember old i8259As have some timing issues
on fast cpus.  Hopefully all the bridge chips are set up correctly ...

> >It is typically much easier to modify PCI device BARS so that they do coincide
> >with the same physical address.   You can control that by using the correct
> >starting address for PCI MEM space in pci_auto.c resource assignment.
> It seems a good way to solve the ioremap problem and X problem.But virt_to_bus
> & bus_to_virt problem remains?
> 

What is the virt_to_bus() problem?  Is the address beyond 512MB (phy addr)? 
If PCI mem (BUS) address is identical to phy addr, you should not have problem
unless the address is beyond 512MB.

BTW, virt_to_bus()/bus_to_virt() are deprecicated.  See
Documentation/DMA-mapping.txt.

Jun