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Re: [patch 1/5] SiByte fixes for 2.6.12

To: Ralf Baechle <ralf@linux-mips.org>
Subject: Re: [patch 1/5] SiByte fixes for 2.6.12
From: Daniel Jacobowitz <dan@debian.org>
Date: Mon, 3 Oct 2005 09:15:52 -0400
Cc: "Maciej W. Rozycki" <macro@linux-mips.org>, Andrew Isaacson <adi@broadcom.com>, linux-mips@linux-mips.org
In-reply-to: <20051001092807.GD14463@linux-mips.org>
Original-recipient: rfc822;linux-mips@linux-mips.org
References: <20050622230042.GA17919@broadcom.com> <Pine.LNX.4.61L.0506231153080.17155@blysk.ds.pg.gda.pl> <20051001092807.GD14463@linux-mips.org>
Sender: linux-mips-bounce@linux-mips.org
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On Sat, Oct 01, 2005 at 10:28:07AM +0100, Ralf Baechle wrote:
> On Thu, Jun 23, 2005 at 12:01:57PM +0100, Maciej W. Rozycki wrote:
> 
> >  Well, the flag is not really to specify whether the common code is to be 
> > used or not.  It's about whether the TLB is like that of the R4k.  
> > Actually it's always been a mystery for me why the common code cannot be 
> > used for the SB1, but perhaps there is something specific that I could 
> > only discover in that "SB-1 Core User Manual" that I yet have to see, 
> > sigh...
> > 
> >  Of course if your TLB is indeed different from that of the R4k, then you 
> > shouldn't be setting cp0.config.mt to 1 in the first place...
> 
> The reason was primarily the tiny bit of extra performance because the
> SB1 doesn't need the hazard handling overhead.  Also tlb-sb1 has a few
> changes that are needed to initialize a TLB in undefined state after
> powerup.  That was needed to run Linux on firmware-less SB1 cores.

FYI, all I have is a piece of hard evidence: this patch was the
difference between not booting and booting for a Sentosa with CFE. 
Which isn't firmwareless and isn't a tiny bit of extra performance
issue.

I'll try to give CVS HEAD a shot this week sometime.

-- 
Daniel Jacobowitz
CodeSourcery, LLC

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