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

To: "Maciej W. Rozycki" <macro@linux-mips.org>
Subject: Re: [patch 1/5] SiByte fixes for 2.6.12
From: Ralf Baechle <ralf@linux-mips.org>
Date: Sat, 1 Oct 2005 10:28:07 +0100
Cc: Andrew Isaacson <adi@broadcom.com>, linux-mips@linux-mips.org
In-reply-to: <Pine.LNX.4.61L.0506231153080.17155@blysk.ds.pg.gda.pl>
Original-recipient: rfc822;linux-mips@linux-mips.org
References: <20050622230042.GA17919@broadcom.com> <Pine.LNX.4.61L.0506231153080.17155@blysk.ds.pg.gda.pl>
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User-agent: Mutt/1.4.2.1i
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.

  Ralf

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