Subject: 32-bit MIPS with > 512mb mem

From: Ralf Baechle <[email-masked]>
Date: Wed, 16 Feb 2000 19:24:27 +0100

Is anybody using 32-bit MIPS CPUs which have more than 512mb of memory or
to be more exact have RAM that isn't accessible via the KSEG0 / KSEG1
window?

So far I haven't ever seen such a machine.  For 64-bit CPUs the right
thing to do is easy - use a 64-bit kernel.  But for 32-bit CPUs the Intel
highmem stuff in the memory managment now gives us a sane way to use
the memory of such configuration with just a little bit of extra code.

So if anybody wants support for such a configuration, please drop me a
note.

Thanks,

  Ralf

---

From: Ralf Baechle <[email-masked]>
Date: Thu, 17 Feb 2000 17:44:32 +0100

On Thu, Feb 17, 2000 at 02:18:16PM +0300, Gleb O. Raiko wrote:

> Not exactly > 512 mb, but related things. On Baget and DECstations, if
> memory serves correctly, there is IO space mapped on KSEG2. Now, Baget
> uses kseg2_allocate_io for it, DECstation also has something similar. IO
> space on Jazz and Co. are located in virtual address window too, can't
> remember where. In princple, access to such IO spaces may be done by
> using highmem.

I've only been refering to RAM where an efficient solution is much more
difficult.

Devices on some R4k machines are special anyway because sometimes they
reside at physical addresses outside the lowest 4gb which means we cannot
even address them using our current page tables.  And changing those in
general isn't a good idea unless we also have RAM at >= 512mb.

  Ralf