From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1756681Ab1KIK5k (ORCPT ); Wed, 9 Nov 2011 05:57:40 -0500 Received: from mail-fx0-f46.google.com ([209.85.161.46]:48172 "EHLO mail-fx0-f46.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1752755Ab1KIK5j (ORCPT ); Wed, 9 Nov 2011 05:57:39 -0500 Subject: Re: [PATCH RFC] virtio-spec: flexible configuration layout From: Sasha Levin To: Pawel Moll Cc: "Michael S. Tsirkin" , Rusty Russell , lkml - Kernel Mailing List , Alexey Kardashevskiy , Amit Shah , Christian Borntraeger , Krishna Kumar , Wang Sheng-Hui , "virtualization@lists.linux-foundation.org" , "kvm@vger.kernel.org" , "avi@redhat.com" In-Reply-To: <1320835653.3259.138.camel@hornet.cambridge.arm.com> References: <87wrbkvh3v.fsf@rustcorp.com.au> <20111101114542.GA13434@redhat.com> <1320150813.3847.24.camel@lappy> <20111101124223.GA14060@redhat.com> <8739e7uy87.fsf@rustcorp.com.au> <20111102233110.GA20289@redhat.com> <20111108214021.GA4538@redhat.com> <1320832502.31056.22.camel@lappy> <20111109101814.GC20612@redhat.com> <1320834017.31056.26.camel@lappy> <1320835653.3259.138.camel@hornet.cambridge.arm.com> Content-Type: text/plain; charset="us-ascii" Date: Wed, 09 Nov 2011 12:55:44 +0200 Message-ID: <1320836144.31056.35.camel@lappy> Mime-Version: 1.0 X-Mailer: Evolution 2.32.3 Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Wed, 2011-11-09 at 10:47 +0000, Pawel Moll wrote: > On Wed, 2011-11-09 at 10:20 +0000, Sasha Levin wrote: > > > > I'm also wondering it it's ok to move virtio configuration out of virtio > > > > space and into PCI space for archs that don't have PCI (such as ARM). > > Just a note - ARM-based chips can by all means have PCI (grep -r PCI > arch/arm/ ;-). The fact is that most of the SOCs available on the market > don't have it, but this is slowly changing. > > The main architectural difference is that ARM doesn't provide separate > I/O space so the PCI I/O space is usually remapped somewhere into normal > address space (grep -r "#define __io_address" arch/arm/) > > > > > Would it mean they get stuck with legacy configuration (and no new > > > > features)? Or is there an alternative for them? > > > > > > The change only affects the layout of virtio PCI. Arches that don't > > > have PCI don't use virtio PCI, presumably? > > > > > > BTW, the spec only covers x86 ATM, this needs to be fixed. > > > > From what I see there is a WIP by Pawel Moll to add > > virtio platform drivers which get virtio working on ARM for example, and > > by Peter Maydell to modify the spec to > > support MMIO access (besides PCI). > > Yep, it's actually already in 3.2-rc1 (drivers/virtio/virtio_mmio.c) and > in the spec (see Appendix X). And actually the control registers layout > I used was originally based on the PCI "legacy" headers (slightly > simplified), but evolved a bit since. My understanding is that the > changes Michael is proposing affect the PCI device interface only so > they shouldn't affect "my" interface. I didn't know it's in already, might be interesting adding support to it to x86 userspace tools. I thought you used the 'legacy' layout, which is why I was worried that these changed might cause problems for you - but from what I see you have a different layout there, so as you said, it shouldn't cause any issues there. > > By the way, I vaguely remember Peter mentioning that he got the PCI > device "experimentally" running some time ago on one of the PCI-enabled > ARM platform models (realview or versatile)... -- Sasha.