From mboxrd@z Thu Jan 1 00:00:00 1970 Received: by oss.sgi.com id ; Wed, 24 Jan 2001 17:09:00 -0800 Received: from gateway-1237.mvista.com ([12.44.186.158]:15609 "EHLO hermes.mvista.com") by oss.sgi.com with ESMTP id ; Wed, 24 Jan 2001 17:08:47 -0800 Received: from mvista.com (IDENT:ppopov@zeus.mvista.com [10.0.0.112]) by hermes.mvista.com (8.11.0/8.11.0) with ESMTP id f0P15gI16997; Wed, 24 Jan 2001 17:05:42 -0800 Message-ID: <3A6F7CB8.322668CF@mvista.com> Date: Wed, 24 Jan 2001 17:09:12 -0800 From: Pete Popov Organization: Monta Vista Software X-Mailer: Mozilla 4.75 [en] (X11; U; Linux 2.2.17 i586) X-Accept-Language: bg, en MIME-Version: 1.0 To: Ralf Baechle CC: Jun Sun , Quinn Jensen , linux-mips@oss.sgi.com Subject: Re: CONFIG_MIPS_UNCACHED References: <3A6E132B.9000103@Lineo.COM> <3A6E1977.2B18484D@mvista.com> <3A6F36B8.4F10759B@mvista.com> <20010124163101.F863@bacchus.dhis.org> Content-Type: text/plain; charset=us-ascii Content-Transfer-Encoding: 7bit Sender: owner-linux-mips@oss.sgi.com Precedence: bulk Return-Path: X-Orcpt: rfc822;linux-mips-outgoing Ralf Baechle wrote: > > On Wed, Jan 24, 2001 at 12:10:32PM -0800, Jun Sun wrote: > > > It is really surprising to know this. It sounds like a CPU bug to me. Can > > some MIPS "gods" clarify if such a behaviour is a bug or allowed? > > > > BTW, the CPU in EV96100 is QED RM7000, I believe. > > If you want to be strictly correct you have to execute the code that > disables caching of KSEG0 in uncached space like KSEG1, then flush the > caches before you can resume execution in KSEG0. Otherwise you might > end up with dirty d-caches which when flushed will overwrite more > uptodate data in memory. The window is very small but yet exists if > things are just right. The EV96100 running Galileo's pmon exhibits exactly this symptom. Pmon apparently sets up kseg0 to cache coherency 3; but eventhough the kernel also sets it to 3, if I don't flush the caches first I end up with overwritten data. A different version of pmon that I have sets kseg0 to 1 (writethrough). Changing that to 3 isn't a problem -- or at least it doesn't seem to cause any problems. Pete