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Re: 64-bit on Cobalt?

To: Ralf Baechle <ralf@oss.sgi.com>
Subject: Re: 64-bit on Cobalt?
From: Carsten Langgaard <carstenl@mips.com>
Date: Mon, 09 Apr 2001 11:37:59 +0200
Cc: John Tobey <jtobey@john-edwin-tobey.org>, linux-mips@oss.sgi.com
References: <20010408184241.A3443@john-edwin-tobey.org> <20010409035453.B774@bacchus.dhis.org>
Sender: owner-linux-mips@oss.sgi.com
Ralf Baechle wrote:

> On Sun, Apr 08, 2001 at 06:42:41PM -0400, John Tobey wrote:
>
> > The CPU is a QED RM5231 (CONFIG_NEVADA) 150MHz.  May I assume that
> > nobody has run a 64-bit kernel on this thing?  The RaQ has no video
> > card but a serial console, PCI, IDE, Ethernet, and special LEDs, panel
> > buttons, and LCD display.  If I can get a 64-bit kernel to boot and
> > prove its existence through any of these devices, I will be drunk with
> > power.
>
> So far the only supported machine by the mips64 kernel is the SGI Origin
> 200 / 2000 series.

I have a QED RM5261 running a bigendian 64-bit kernel on our Malta board (it
got a serial console, PCI, IDE, Ethernet).
I haven't send the patch to Ralf yet, but you can get a snapshot at our
kernel sources at
ftp://ftp.mips.com/pub/linux/mips/kernel/2.4/src/linux-2.4.1.mips-src-01.00.tar.gz

Hope it helps you.

>
> > The reason I want 64 bits is that I (a) want a challenge, (b) plan to
> > write an application that uses a sparse address space (40 bits is
> > better than 31), (c) plan to outlive the 31-bit time_t, and (d) am
> > p.o.ed at having bought the thing based on misleading advertising that
> > mentioned a 64-bit processor but not the 32-bit OS.
>
> > Big/little endian macht nichts.  I guess big will be easier, and I'm
> > not concerned with running any existing 32-bit binaries.
>
> Go for little endian because the firmware is little endian; supporting
> ``other-endian'' for userspace would be unecessary extra pain.  We already
> have suport for 32-bit binaries in the 64-bit kernel; in fact ALL
> software we run on 64-bit kernels is 32-bit.
>
> 32-bit wasn't only the easy thing to do - it's also the more efficient
> thing for most software which doesn't need 64-bit registers or 64-bit
> address space.  For a system with a dog slow 32-bit memory bus such as
> the Qube 64-bit kernels would mean a dramatic slowdown.
>
> I admit it's interesting though, mostly for engineering reasons, not
> as a platform.
>
> > I imagine that I would start by grafting Cobalt's peripheral support
> > code from arch/mips/cobalt (now defunct) and include/asm-mips/cobalt.h
> > into the mips64 tree from cvs@oss.sgi.com:/cvs/linux.
>
> Somebody else was already working on upgrading the Cobalt kernel to 2.4.
>
>   Ralf

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