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Date: Sun, 29 Apr 2001 16:05:39 -0500
From: Steffen Persvold <sp@scali.no>
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To: =?iso-8859-1?Q?G=E9rard?= Roudier <groudier@club-internet.fr>
CC: lkml <linux-kernel@vger.kernel.org>, davej@suse.de, troels@thule.no
Subject: Re: ServerWorks LE and MTRR
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G?rard Roudier wrote:
> 
> On Sun, 29 Apr 2001, Steffen Persvold wrote:
> 
> > Hi all,
> >
> > I just compiled 2.4.4 and are running it on a Serverworks LE motherboard.
> > Whenever I try to add a write-combining region, it gets rejected. I took a peek
> > in the arch/i386/kernel/mtrr.c and found that this is just as expected with
> > v1.40 of the code. It is great that the mtrr code checks and prevents the user
> > from doing something that could eventually lead to data corruption. Using
> > write-combining on PCI acesses can lead to this on certain LE revisions but
> > _not_ all (only rev < 5). Therefore please consider my small patch to allow the
> > good ones to be able to use write-combining. I have several rev 06 and they are
> > working fine with this patch.
> 
> You wrote that 'only rev < 5' can lead to data corruption, but your patch
> seems to disallow use of write combining for rev 5 too.
> 
> Could you clarify?

Oops just a typo, it should be <= 5. The patch is correct.

> 
>   G?rard.
> 
> PS:
> >From what hat did you get this information ? as it seems that ServerWorks
> require NDA for letting know technical information on their chipsets.
> 

I've learned it the hard way, I have two types : Compaq DL360 (rev 5) and a
Tyan S2510 (rev 6). On the compaq machine I constantly get data corruption on
the last double word (4 bytes) in a 64 byte PCI burst when I use write
combining on the CPU. On the Tyan however the transfer is always ok.

-- 
 Steffen Persvold                        Systems Engineer
 Email  : mailto:sp@scali.com            Scali AS (http://www.scali.com)
 Norway : Tel  : (+47) 2262 8950         Olaf Helsets vei 6
          Fax  : (+47) 2262 8951         N-0621 Oslo, Norway

 USA    : Tel  : (+1) 713 706 0544       10500 Richmond Avenue, Suite 190
                                         Houston, Texas 77042, USA
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