From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from motgate3.mot.com (motgate3.mot.com [144.189.100.103]) by ozlabs.org (Postfix) with ESMTP id DADCE2BDEB for ; Sat, 13 Nov 2004 03:27:25 +1100 (EST) In-Reply-To: References: Mime-Version: 1.0 (Apple Message framework v619) Content-Type: text/plain; charset=ISO-8859-1; format=flowed Message-Id: <28CBA210-34C4-11D9-8B98-000393DBC2E8@freescale.com> From: Kumar Gala Date: Fri, 12 Nov 2004 10:01:48 -0600 To: Cc: linuxppc-embedded@ozlabs.org Subject: Re: PowerPC MMU questions List-Id: Linux on Embedded PowerPC Developers Mail List List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , On Nov 11, 2004, at 9:36 PM, Jeff Domogala wrote: > Folks, > > I am dealing with a PowerPC 7455.=A0 Here is my understanding = regarding=20 > the > MMU translation order:=A0 If the address is covered in a BAT, that = BAT > translation is in effect.=A0 If there is no BAT entry, then the page=20= > tables > are used to translate the address.=A0 If there is no page table = entry,=20 > an > exception is thrown and the exception handler for the miss needs to=20= > add a > new PTE.=A0 So, correct me if I'm wrong in my translation. > > Now, The system starts up with BAT entries to get the system off the=20= > ground. > I have equivalent BAT entries for the instruction and data sides.=A0 = I=20 > also > have the L1 I and D caches on as well as the L2 cache (I and D=20 > mode).=A0 The > reason for using the BATs is to create non-cached I/O regions until=20= > the MMU > PTEs are populated.=A0 Once the MMU PTEs are setup, the caches are=20 > flsuhed and > disabled, the MMU is disabled, the BATS disabled, the MMU re-enabled=20= > and the > caches re-enabled.=A0 So here are my questions: > > 1. Is it ok to have the same I and D BAT entries? Yes, the I-BAT will be used for translations on instruction fetches,=20 the D-BAT will be used on data accesses (ld/st instructions). > 2. Is it ok to setup the initial MMU PTEs with the BATs enabled or=20 > should > the caches be disabled and MMU disabled during the PTE setup? There should be no harm setting up MMU PTEs with BATs enabled, as you=20 said the BATs will take preference over the PTEs > 3. Is there some other esource out there (mailing list or otherwise)=20= > that I > should be addressing these questions to? This is as good as any, assuming your using linux :) Also, the=20 Freescale website has a number of App Notes on the various PPC MMUs and=20= an email support address risc10@freescale.com - kumar