From mboxrd@z Thu Jan 1 00:00:00 1970 From: Rusty Russell Subject: Re: [PATCH] virtio-spec: Define virtio-mmio registers as LE Date: Thu, 07 Mar 2013 17:36:13 +1100 Message-ID: <871ubryaw2.fsf@rustcorp.com.au> 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> Mime-Version: 1.0 Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: 7bit Return-path: In-Reply-To: <1362582615.3105.45.camel@hornet> List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Sender: virtualization-bounces@lists.linux-foundation.org Errors-To: virtualization-bounces@lists.linux-foundation.org To: Pawel Moll Cc: "Michael S. Tsirkin" , "linux-kernel@vger.kernel.org" , "virtualization@lists.linux-foundation.org" List-Id: virtualization@lists.linuxfoundation.org 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.