[C] From: Mark Montague
Date: 18 Mar 1999 20:51:54 -0800
Subject: Re: Linux memory recoginition

"Jan Juraj (George) Frajkor" writes:

> Bryan Taylor wrote:
> 
> > 1. Was there ever a way of getting linux to see the entire 20Mb
> > rather than only 16Mb? (I'm still using Slackware 3.0)
> > I realise this is a generic Compaq problem,
> > since I used to use a Prolinea at work with Redhat 4.2 that only saw
> > 16 of its 32 Mb.
> 
>   My understanding is that this problem was fixed by the sofpaq SP1992
> which you can download from Compaq.    This certainly works for WIntel
> processors and programs.   Is there some reason linux would not
> recognize this bios patch?  You now have me worried as I was about to
> install linux in place of my Wintel stuff.

I installed the patch before I put in my 16MB module, so it doesn't
help with linux, exactly; it's still better to see ~16MB than 12MB,
though. The BIOS does count up 20MB in the memory test phase, though,
which is what I've imagined that will correct.

I've seen a lot of BIOS issues where linux won't recognize the correct
memory info; apparently, it's common for BIOSes to do "nonstandard"
things, so I've seen a lot of new-ish desktops that only report 64MB,
so linux needs the mem=256M or what have you line. It works fine with
that line, however. There was talk of a patch on the linux-kernel
mailing list to try to autodetect memory with some "newer" method, but
there was some debate as to whether this was a good thing or
not... it's possible it'd be bad for us old computer users, in fact.

Also, the book I referred to earlier was

_Linux Device Drivers_, by Alessandro Rubini, O'Reilly & assoc 1998
ISBN 1-56592-292-1

on pages 173-175, he discusses "ISA memory above 1MB" and has the code
snip below, for a hole at 15MB-16MB at kernel 2.0.29, this goes into
arch/i386/mm/init.c in mem_init:

---------------------- cut here ----------------------
while ( start_mem < high_memory ) {
  if ( start_mem >= 0xf00000 && start_mem < 0x1000000 ) {
    /* keep it reserved, and prevent counting as data */
    reservedpages++; datapages--;
  }
  else
    clear_bit(PG_reserved. &mem_map[MAP_NR(start_mem)].flags);
  start_mem += PAGE_SIZE;
}
---------------------- cut here ----------------------

---> caution: copied by hand. may contain typos.

I'm about to try compiling a 2.2.3 kernel with my own version of this
patch; we'll see how it works...

[C] Subject: Re: Linux memory recoginition
From: Mark Montague 
Date: 18 Mar 1999 03:07:58 -0800
Subject: Linux 20Mb woes

"Bryan Taylor" writes: 

> 1. Was there ever a way of getting linux to see the entire 20Mb rather
> than only 16Mb? (I'm still using Slackware 3.0) I realise this is a
> generic Compaq problem,
> since I used to use a Prolinea at work with Redhat 4.2 that only saw 16
> of its 32 Mb.

There is an easy fix for this, but with a very annoying new problem: you
can add a mem=20M line to your boot, via adding 

append="mem=20M"

to the appropriate place in your lilo.conf. However, this hoses your
pcmcia badly, I believe because the pcmcia controller wants memory-mapped
i/o in the <16M region. 
The symptom is a hard lock-up when a card is inserted, or when the pcmcia
stuff is started at boot time.

I do have two possible kernel hacks which may fix this, but I haven't
tried them yet (I'm thinking of waiting until the 2.2.* series stabilizes
more before trying).

One is the "BigPhysicalArea" patch, which comes in the Debian default
kernel packages. Unfortunately, this puts the reserved area where it wants
to; I don't think it's possible to request a hole where the pcmcia stuff
wants it (maybe this is OK; the ways of the pcmcia chipset are strange and
mysterious, and largely unknown to me...) 

The more promising approach is that in the O'Riley book on writing linux
device drivers, it's mentioned (with a code example) that it's possible to
mark some pages as unusable at boot time, and has code to do exactly that,
albeit with an outdated kernel. I'll probably be building an aero-specific
kernel with that in mind at some point in the not-too-distant future. When
I'm in work tomorrow, I'll try to remember to post the book's exact title
and author, and maybe the code snippet as well.

Also, in the mean time, there is also a patch floating around somewhere
that allows not-normally-usable RAM to be used as a really-fast swap
"disk." I could probably find the URL with a little effort, but if I'm
really going to spend a little effort on the problem, I might as well try
building the 2.2.3 kernel with the reserved-memory hack. Has anyone out
there in aeroland tested the 2.2.* series with the aero yet? The early
ones had some reports of APM weirdness, but the 2.2.3 release seems much
more reliable on my desktop, and I'm seeing less horror stories on the
linux-kernel mailing list since 2.2.3 as well. - M

[C]
Linux works on the Aero. There are a few other resources for info on how to
install Linux, and its nuances with the Aero. One of these sites on WWW is
http://domen.uninett.no/~hta/linux/aero-faq.html We definitely recommend that
you check this out if you want to run Linux.

[C]
Date: Mon, 15 Dec 1997 10:23:51 +0100 (MET)
From: Javier Hernandez <fjherna@ctv.es>
Subject: Re: 20M Memory settings for Linux

On Fri, 5 Dec 1997, Brandon Hines wrote:
> I am looking for the correct setting so that Linux can recognize 20meg ram.
> Did anybody archive the information?  I tried MAN and the FAQ but could not
> find the references.  Javier, are you out there?  I remember you having this
> down to a science.
 
The problem is not still solved.
I did tried different lines with LILO and with loadling but with all
them I got problems, sooner or later.
More than problems what I got was "inestability"; for example the most
"fine" line I got was with "mem=20416k" at LILO.
It works fine and you get more than 16MB of RAM being recognized but
you can expect to have "extranges behaviours" sometimesi (overall if
you get at internet).

Just try it

I think the Aero was not ready for 20MB RAM, only for 16MB maximum.
Some person mentioned it at this list, sometime ago refering a
conversation with a person from COMPAQ. In fact I think, COMPAQ never
offer to sell 16MB of RAM upgrade, only 8MB maximum.