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Re: [patch] linux: New style IRQs for DECstation

To: "Maciej W. Rozycki" <macro@ds2.pg.gda.pl>
Subject: Re: [patch] linux: New style IRQs for DECstation
From: Jun Sun <jsun@mvista.com>
Date: Mon, 08 Apr 2002 11:25:54 -0700
Cc: Ralf Baechle <ralf@uni-koblenz.de>, linux-mips@fnet.fr, linux-mips@oss.sgi.com
References: <Pine.GSO.3.96.1020408195036.26107N-100000@delta.ds2.pg.gda.pl>
User-agent: Mozilla/5.0 (X11; U; Linux i686; en-US; rv:0.9.4) Gecko/20011126 Netscape6/6.2.1
Maciej W. Rozycki wrote:

On Mon, 8 Apr 2002, Jun Sun wrote:


What is the intention of introducing MIPS_CPU_FPUEX? It seems an overkill if it is just needed by DecStation. How many CPUs really need this?


 It's needed by any system using a (logically) external FPU.  If set it
means there is no need to install a special FPU exception handler using a
general-purpose interrupt line. It's a generic flag.
 Even if it's only of limited use now, it is not an excuse for not writing
clean code.  I'm afraid the current mess within the MIPS port is a result
of people trying to think locally and I'm trying to avoid it.  Are there
any trade-offs of this flags you see and I don't?  I'm willing to change
the code if there really are.


Generally interrupt dispatching belongs to machine/board-specific code. So I think FPU exeption through an interrupt is probably best handled within DEC's code, instead of being generalized to the common code.

In addition, conceptional you might have a system where FPU exception is handled through an interrupt and yet CPU has FPU exception.

Of course abstraction and generalization can happen later when it becomes obvious. It is just not obvious, at least to me.

Jun




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