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Re: [MIPS] FPU emulator: allow Cause bits of FCSR to be writeable by ctc

To: "Kevin D. Kissell" <kevink@paralogos.com>
Subject: Re: [MIPS] FPU emulator: allow Cause bits of FCSR to be writeable by ctc1
From: Ralf Baechle <ralf@linux-mips.org>
Date: Wed, 5 May 2010 10:11:59 +0100
Cc: Shane McDonald <mcdonald.shane@gmail.com>, linux-mips@linux-mips.org, Atsushi Nemoto <anemo@mba.ocn.ne.jp>
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On Wed, May 05, 2010 at 12:48:33AM -0700, Kevin D. Kissell wrote:

> I'm glad to hear that the patch is functional.  It was pretty clear that
> it would solve your problem, but I was concerned that the inability to
> write the Cause bits was done as a way around some other problem. 
> Someone went to a certain amount of trouble to not accept them as
> inputs, in violation of spec.  I just looked back, and the bug was
> introduced as part of a patch of Ralf's from April 2005 entitled "Fix
> Preemption and SMP problems in the FP emulator".  It's unlikely that
> overriding CTC semantics actually fixed any underlying problems, but it
> may have masked symptoms of problems that we can only hope have been
> fixed in the mean time. Anyone run this patch on an FPUless SMP?   Oh,
> for a 34Kf with a bunch of TCs! ;o)

That's commit ID 72402ec9efdb2ea7e0ec6223cf20e7301a57da02 and the patch
was comitted during the CVS days which only records the comitter but not
the author.  The actual author is Atsushi Nemoto.

  Ralf

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