Re: [parisc-linux] Linux only see 2Gb of ram of N4k

[Grant Grundler <grundler@parisc-linux.org>]

On Fri, Feb 20, 2004 at 06:21:40PM +0000, Matthew Wilcox wrote:
> Unlikely.  As I recall, the N4k diagram looks like this:

Beautiful diagram! (I'm saving that one)
And I confirmed it is correct in case anyone had doubts.
(I did)

> So the RAM is uniformly-accessible from all CPUs, but the IO is not.

I don't think there is much penalty for CPU's to access MMIO space
on "the other side". MMIO reads are so expensive anyway, I'd doubt
it would make that much difference.

> If you look at pat_memconfig() in arch/parisc/kernel/inventory.c, you'll
> see how we try to figure out what memory ranges are in the machine.
> Want to try debugging that, see what's being reported by firmware?

I'm pretty sure it will look like this:
RAM      Phys Address
0-2GB -> 0-2GB
      -> 2-4GB I/O Space (mostly PCI MMIO)
2-4GB -> 4-6GB (courtesy of the memory controller)

The N-class was the first box which has an I/O hole from 2-4GB
physical address range. I hope Joel will be able to confirm this.
If not, I likely have documentation to confirm this.

grant