Subject: Re: Status of the Indigo2 R10K port?
To: Mark KAHRS <email@example.com>
From: Christopher SEKIYA <firstname.lastname@example.org>
Date: 08/23/2004 21:05:53
On Sun, Aug 22, 2004 at 02:42:20PM -0400, Steve Rumble wrote:
> Once that's running it may be fairly trivial to get a 32bit kernel booted,
> but those could be famous last words.
It's possible to design a MIPS-IV machine such that all of the critical goo
(ARCS, I/O) can be accessed from both 64-bit and 32-bit mode. In fact, it's
downright easy -- there's a wonderful example in "See MIPS Run".
Those who have coded for NetBSD/sgimips have learned that SGI had a rather
interesting attitude towards design. It should come as no surprise, then,
that the IP30 has placed ARCS in space that can be accessed _only_ in 64-bit
mode. I'm not entirely sure that all of the critical I/O lives entirely in
32-bit space, either -- crossbow is a very odd beast.
It's possible to put a jump table in 32-bit-accessible space that will jump
up to the real ARCS space. I haven't made it work yet, though.
Then we have the netbooting issue. If we're going to use a 64-bit bootloader
to load a 32-bit kernel, the bootloader _must_ be able to talk to the NIC,
and the DMA glue for said NIC. There aren't any ARCS routines for network
interfaces, AFAICT (though I would _love_ to be proved wrong).
I'm mostly convinced that the 64-bit SGI machines (Octane, Power Indigo)
will need 64-bit kernels. There's all sorts of nasty 32-bit assumptions in
arch/mips that I'm trying to work thorough.
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