Subject: Re: Relocating interrupt vectors in ppc440?

From: Matt Porter <[email-masked]>
Date: Thu, 27 Jan 2005 11:16:15 -0700

On Thu, Jan 27, 2005 at 10:05:33AM -0800, Shawn Jin wrote:
> Hi,
> 
> Do interrupt vectors locate at low addresses physically in ppc440?

Yes.

> >From the processor's user manual I understand that the base address of
> interrupt vectors actually can be anywhere, set by IVPR. Also from
> head_44x.S I found the following comments
> 
> /*
>  * The Book E MMUs are always on so we don't need to handle
>  * interrupts in real mode as with previous PPC processors. In
>  * this case we handle interrupts in the kernel virtual address
>  * space.
>  *
>  * Interrupt vectors are dynamically placed relative to the
>  * interrupt prefix as determined by the address of interrupt_base.
>  * The interrupt vectors offsets are programmed using the labels
>  * for each interrupt vector entry.
>  *
>  */
> 
> The address of interrupt_base is 0xc0000224 in the image I built,
> which is a virtual address from kernel point of view. What's the
> corresponding physical address? Is it my SDRAM's physical base address
> + 0x224 (the offset)?

Yes.

> Assumed that the interrupt vectors locate at the low address space
> physically and given that there is 2GB SDRAM shared by two ppc440
> cores, can one of linux kernels run at the top of 1GB space? This
> means the interrupt vectors for this copy need to move to upper 1GB.
> Each core runs a copy of linux kernel independently.

Yes, you'd have to do something like the APUS code does by settings
PPC_MEMSTART appropriately for the second processor. Also, of course
limiting the memory on the first processor to 1GB. There's probably
a lot of fall out from PPC_MEMSTART being non-zero. I seem to
recall lots of assumptions about PPC_MEMSTART being at zero as
I was doing the ppc440 core work. You'll have to audit all the
MM paths for these assumptions, but it can be done.

> Any ideas about relocating interupt vectors in ppc440?

One idea is that if you really don't have to do it, then don't. :)

-Matt