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Re: [patch] linux 2.4.5: Export mips_machtype

To: "Gleb O. Raiko" <raiko@niisi.msk.ru>
Subject: Re: [patch] linux 2.4.5: Export mips_machtype
From: "Maciej W. Rozycki" <macro@ds2.pg.gda.pl>
Date: Thu, 23 Aug 2001 17:59:51 +0200 (MET DST)
Cc: linux-mips@fnet.fr, linux-mips@oss.sgi.com
In-reply-to: <3B84EB2C.7643F00B@niisi.msk.ru>
Organization: Technical University of Gdansk
Sender: owner-linux-mips@oss.sgi.com
On Thu, 23 Aug 2001, Gleb O. Raiko wrote:

> In order to read a PCI ID, you need to know how to do it. In pc world,
> you may rely on configuation access types, at least, ports are known. On
> other arches, you need to know where such "ports" are. Even if hardware
> supports, say, configuration type 1 accesses, developers are free to put
> port addresses anywhere.

 Yep, I see.  MIPS is quite special here, because, unlike for Alphas,
PowerPCs, SPARCs, etc. there is a couple of independend vendors making
systems, so there is no single way of obtaining a system ID.  So you need
to know how to access chipset from elsewhere.

> >  How do you set up mips_machtype on your system in the first place?  At
> > kernel_entry the code does not know what machine it's running on anyway,
> > so it has to set mips_machtype based on a detection algorithm.
> 
> First, mips_machtype is accessed far later than kernel_entry is

 That's quite obvious -- nothing can be done in Linux earlier. ;-)  But
you need to initialize mips_machtype somehow.

> executed. Personally, I am lucky :-), I may read firmware environment
> variables.

 Well, other system might as well (e.g. DECstations can), but that doesn't
solve the problem -- to access firmware variables you need to know which
kind of firmware you are on. 

-- 
+  Maciej W. Rozycki, Technical University of Gdansk, Poland   +
+--------------------------------------------------------------+
+        e-mail: macro@ds2.pg.gda.pl, PGP key available        +


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