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RE: MIPS 64?

To: "Jun Sun" <jsun@mvista.com>, "Daniel Jacobowitz" <dan@debian.org>
Subject: RE: MIPS 64?
From: "Matthew Dharm" <mdharm@momenco.com>
Date: Wed, 15 May 2002 15:16:29 -0700
Cc: "Linux-MIPS" <linux-mips@oss.sgi.com>
Importance: Normal
In-reply-to: <3CE2DA46.3070402@mvista.com>
Sender: owner-linux-mips@oss.sgi.com
I personally think it's long overdue that we really invest some
time/effort in the 64-bit version.  I mean, anything past 0.5 GiB is
really a hack on 32-bit....

I, for one, am willing to lend a pair of hands to this... but I need
to know what needs doing, first.

Could someone give me an overview of how you're supposed to do a
handoff between a 32-bit loader and a 64-bit app?  I'm guessing there
has to be a way to do it, but what I do know about the 64-bit stuff
doesn't show me how this is accomplished (I have visions of UX bits
floating in my head...)

Matt

--
Matthew D. Dharm                            Senior Software Designer
Momentum Computer Inc.                      1815 Aston Ave.  Suite 107
(760) 431-8663 X-115                        Carlsbad, CA 92008-7310
Momentum Works For You                      www.momenco.com

> -----Original Message-----
> From: owner-linux-mips@oss.sgi.com
> [mailto:owner-linux-mips@oss.sgi.com]On Behalf Of Jun Sun
> Sent: Wednesday, May 15, 2002 3:00 PM
> To: Daniel Jacobowitz
> Cc: Matthew Dharm; Linux-MIPS
> Subject: Re: MIPS 64?
>
>
> Daniel Jacobowitz wrote:
>
> > On Wed, May 15, 2002 at 02:34:47PM -0700, Matthew Dharm wrote:
> >
> >>So... I'm looking at porting Linux to a system with 1.5GiB of RAM.
> >>That kinda blows the 32-bit MIPS port option right out of
> the water...
> >>
> >
> > Not unless you count bits differently than I do... 32-bit
> is 4 GiB.  Is
> > there any reason MIPS has special problems in this area?
> >
>
>
> MIPS has lower 2GB fixed for user space.  Then you have
> kseg0, .5GB for cached
> physical address 0-0.5GB, and kseg1, 0.5GB uncached mapping
> of the same area.
>   You can map another 1GB of RAM into kseg2/3, but you will
> then have no space
> left for IO.
>
> So you really can't do 1.5GB on 32 bit kernel.
>
> It is interesting that PPC allows one to adjust user space
> size and kernel
> space size.  So on PPC you can get up to 2.5GB system RAM
> with 1GB user space.
>
> Back to 64bit port, it seems to me much of the 32bit work
> we have done in the
> past a year or so needs to be moved over.  Or better yet,
> if we can clean up
> integer/long issues, we might be able to use 32bit kernel
> code straight for
> 64bit kernel.
>
>
> Jun
>
>


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