Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1753109Ab3CGHEu (ORCPT ); Thu, 7 Mar 2013 02:04:50 -0500 Received: from ozlabs.org ([203.10.76.45]:60166 "EHLO ozlabs.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751352Ab3CGHEs (ORCPT ); Thu, 7 Mar 2013 02:04:48 -0500 From: Rusty Russell To: Pawel Moll Cc: Marc Zyngier , "virtualization\@lists.linux-foundation.org" , "linux-kernel\@vger.kernel.org" , "Michael S. Tsirkin" Subject: Re: [PATCH] virtio-spec: Define virtio-mmio registers as LE In-Reply-To: <1362582615.3105.45.camel@hornet> References: <87wqubkalj.fsf@rustcorp.com.au> <1360839247-9131-1-git-send-email-pawel.moll@arm.com> <513085EA.8070007@arm.com> <1362135005.3052.26.camel@hornet> <51308F22.7040303@arm.com> <1362141432.3052.28.camel@hornet> <87fw0ad7sr.fsf@rustcorp.com.au> <1362582615.3105.45.camel@hornet> User-Agent: Notmuch/0.14 (http://notmuchmail.org) Emacs/23.4.1 (i686-pc-linux-gnu) Date: Thu, 07 Mar 2013 17:36:13 +1100 Message-ID: <871ubryaw2.fsf@rustcorp.com.au> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 1812 Lines: 43 Pawel Moll writes: > On Tue, 2013-03-05 at 00:11 +0000, Rusty Russell wrote: >> Pawel Moll writes: >> > On Fri, 2013-03-01 at 11:21 +0000, Marc Zyngier wrote: >> >> > Having said that, Rusty was contemplating enforcing LE config space in >> >> > the new PCI layout... >> >> >> >> I wouldn't complain about that, and would like to see a similar thing on >> >> MMIO. >> > >> > Wherever PCI goes, MMIO follows :-) >> >> Yes, but if you switch from 'guest-endian' to 'little-endian' how will >> you tell? For PCI, we'd detect it by using the new layout. > > The version register/value. At some point of time there will be a > new(ish) MMIO layout anyway to deal with 64-bit addresses, replacing the > ring page number with two 32-bit hi/lo physical address registers. This > was discussed not long after the driver got merged... As long as you have a plan for older guests... >> I'd rather you specify MMIO as little endian, and we fix the kernel >> config accessors to be endian aware (ie. 8, 16, 32, 64-bit accessors). >> Since noone BE is using MMIO right now, it's safe... > > That's absolutely fine with me, however I don't see anything I could do > in the virtio_mmio driver and spec - the virtio_config_ops specifies > get/set as void * operations and I simply do byte-by-byte copy. Have I > missed some config/endianess/PCI related discussion? Yes, that's exactly what I mean, they'd have to be split into 8/16/32/64 accessors. Which would do byte-by-byte for PCI. The spec can simply be updated. Cheers, Rusty. -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/