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Re: Almost got 2.1.14.2 to a patchable stage...

To: linux-mips
Subject: Re: Almost got 2.1.14.2 to a patchable stage...
From: Dom Sweetman <dom@algor.co.uk>
Date: Fri, 11 Apr 1997 11:34:27 +0100 (BST)
In-reply-to: <199704110737.DAA00869@jenolan.caipgeneral>
References: <199704110721.HAA12436@suede.sw.oz.au> <199704110737.DAA00869@jenolan.caipgeneral>
David S. Miller (davem@jenolan.rutgers.edu) writes:

> The whole mips[1234] ordeal is the one thing which upset me greatly
> about the MIPS processor line, this is the single one thing which
> makes a true "all in one" MIPS/Linux kernel damn near impossible.

It's worse than that; MIPS[1234] only prescribes the user-level
behaviour of the CPU.  The bits of the CPU which only the kernel deals
with (what MIPS calls "co-processor 0") are implementation dependent.
The R5000 is rather different from the R10000 at this level, although
they both implement MIPS-4.

It's also better than that, in that:

o All Linux-capable MIPS-1 CPUs are pretty much compatible.

o There are no MIPS-2 CPUs (it was only invented for the ECL R6000,
  which didn't have a very big sale)

o All Linux-capable MIPS-3 CPUs are readily driven with the same
  software.  Some detailed differences (R4400 likes more nops than
  R4600 sometimes), but nothing serious.

You will need ifdefs for MIPS-1 vs MIPS-3 in any code which messes
with the interrupt levels or TLB.

And there again it's worse, because you'll search in vain for any
systematic documentation about this.

Dominic Sweetman
dom@algor.co.uk

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