From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from e23smtp02.au.ibm.com (E23SMTP02.au.ibm.com [202.81.18.163]) (using TLSv1 with cipher DHE-RSA-AES256-SHA (256/256 bits)) (Client CN "e23smtp02.au.ibm.com", Issuer "Equifax" (verified OK)) by ozlabs.org (Postfix) with ESMTPS id 1385DDDE10 for ; Tue, 8 Apr 2008 14:18:42 +1000 (EST) Received: from d23relay03.au.ibm.com (d23relay03.au.ibm.com [202.81.18.234]) by e23smtp02.au.ibm.com (8.13.1/8.13.1) with ESMTP id m384IgGF013312 for ; Tue, 8 Apr 2008 14:18:42 +1000 Received: from d23av01.au.ibm.com (d23av01.au.ibm.com [9.190.234.96]) by d23relay03.au.ibm.com (8.13.8/8.13.8/NCO v8.7) with ESMTP id m384IbPs528432 for ; Tue, 8 Apr 2008 14:18:37 +1000 Received: from d23av01.au.ibm.com (loopback [127.0.0.1]) by d23av01.au.ibm.com (8.12.11.20060308/8.13.3) with ESMTP id m384IbRH024524 for ; Tue, 8 Apr 2008 14:18:38 +1000 Date: Tue, 8 Apr 2008 14:16:03 +1000 From: David Gibson To: Hollis Blanchard Subject: Re: [PATCH 2 of 3] [KVM] Add DCR access information to struct kvm_run Message-ID: <20080408041603.GB18501@localhost.localdomain> References: <200804072225.33040.hollisb@us.ibm.com> <20080408035441.GA18501@localhost.localdomain> <200804072306.10684.hollisb@us.ibm.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii In-Reply-To: <200804072306.10684.hollisb@us.ibm.com> Cc: kvm-devel@lists.sourceforge.net, linuxppc-dev@ozlabs.org, kvm-ppc-devel@lists.sourceforge.net List-Id: Linux on PowerPC Developers Mail List List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , On Mon, Apr 07, 2008 at 11:06:10PM -0500, Hollis Blanchard wrote: > On Monday 07 April 2008 22:54:41 David Gibson wrote: > > On Mon, Apr 07, 2008 at 10:25:32PM -0500, Hollis Blanchard wrote: > > > On Monday 07 April 2008 20:11:28 David Gibson wrote: > > > > On Mon, Apr 07, 2008 at 03:53:33PM -0500, Hollis Blanchard wrote: > > > > > 1 file changed, 7 insertions(+) > > > > > include/linux/kvm.h | 7 +++++++ > > > > > > > > > > > > > > > Device Control Registers are essentially another address space found > > > > > on PowerPC 4xx processors, analogous to PIO on x86. DCRs are always > > > > > 32 bits, and are identified by a 32-bit number. > > > > > > > > Well... 10-bit, actually. > > > > > > The mtdcrux description in the ppc440x6 user manual says the following: > > > > > > Let the contents of register RA denote a Device Control Register. > > > The contents of GPR[RS] are placed into the designated Device Control > > > Register. > > > > > > I take that to mean that we must worry about 32 bits worth of DCR > > > numbers. Perhaps I should say "no more than" rather than "always". > > > > I think that's less misleading. mtdcrux is very new, anything which > > only has the mtdcr instruction certainly can't take DCR numbers above > > 10 bits, and I would expect that even on chips with mtdcrux the DCR > > bus is probably still only 10-bits, although it could be extended. > > We're defining a kernel/userspace interface here, and since the hardware is > capable of 32-bit DCR numbers, I don't think it makes any sense to not > support that. Also, we would just end up placing that number into a u32 > anyways, so... :) Oh, of course you should represent it as a u32 and support 32-bit addresses, it's only the patch comment I'm objecting to. -- David Gibson | I'll have my music baroque, and my code david AT gibson.dropbear.id.au | minimalist, thank you. NOT _the_ _other_ | _way_ _around_! http://www.ozlabs.org/~dgibson