kernel won't boot on a Cyrix MediaGXm (Geode )

From: Samuel Sieb
Date: Mon Jul 21 2008 - 01:12:28 EST

I have a computer here with a CPU that the BIOS identifies as:
Cyrix MediaGXm/Cx5530 Unicorn Revision 1.19.3B

kernel 2.6.14 identifies it as:
vendor_id : Geode by NSC
cpu family : 5
model : 9
model name : Geode(TM) Integrated Processor by National Semi
stepping : 1

I can't boot any kernel later than 2.6.22 on it. Anything later either hangs or gives random kernel panics while booting. I tracked down the problem to a specific commit:

commit f25f64ed5bd3c2932493681bdfdb483ea707da0a
Author: Juergen Beisert <juergen@xxxxxxxxxxxxxx>
Date: Sun Jul 22 11:12:38 2007 +0200

x86: Replace NSC/Cyrix specific chipset access macros by inlined functions.

Reversing the patch (compensating for kernel changes) let me boot a 2.6.25 kernel. I realize the patch is supposed to fix something that didn't work right, but I didn't have a problem before and I do now. :-)
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