From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from eggs.gnu.org ([2001:4830:134:3::10]:46192) by lists.gnu.org with esmtp (Exim 4.71) (envelope-from ) id 1ZyGWm-0001YF-Ct for qemu-devel@nongnu.org; Mon, 16 Nov 2015 04:56:49 -0500 Received: from Debian-exim by eggs.gnu.org with spam-scanned (Exim 4.71) (envelope-from ) id 1ZyGWj-0003UO-6z for qemu-devel@nongnu.org; Mon, 16 Nov 2015 04:56:48 -0500 Received: from mx1.redhat.com ([209.132.183.28]:51964) by eggs.gnu.org with esmtp (Exim 4.71) (envelope-from ) id 1ZyGWj-0003TR-1G for qemu-devel@nongnu.org; Mon, 16 Nov 2015 04:56:45 -0500 References: <1447601946-31248-1-git-send-email-marcel@redhat.com> <5649966C.7070702@redhat.com> <5649A770.5070908@redhat.com> From: Paolo Bonzini Message-ID: <5649A857.406@redhat.com> Date: Mon, 16 Nov 2015 10:56:39 +0100 MIME-Version: 1.0 In-Reply-To: <5649A770.5070908@redhat.com> Content-Type: text/plain; charset=windows-1252 Content-Transfer-Encoding: 7bit Subject: Re: [Qemu-devel] [PATCH V2 0/4] hw/pcie: Multi-root support for Q35 List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , To: Marcel Apfelbaum , qemu-devel@nongnu.org Cc: imammedo@redhat.com, rth@twiddle.net, kraxel@redhat.com, ehabkost@redhat.com, mst@redhat.com On 16/11/2015 10:52, Marcel Apfelbaum wrote: > On 11/16/2015 10:40 AM, Paolo Bonzini wrote: >> >> >> On 15/11/2015 16:39, Marcel Apfelbaum wrote: >>> Addressed Gerd Hoffmann comments: >>> - Added x-enable-internal-bridge compat property to keep the PCI >>> bridge for older machine to avoid breaking migration. >> >> This will break PXB command lines written for "-M pc" in QEMU <= 2.5. >> Technically there's no prohibition against doing so, but we've never >> done it; I'm not sure why we should start doing so now. > > Hi Paolo, > > Can you please explain how does it break the command line? > > For QEMU < 2.5 we automatically have the x-enable-internal-bridge > compat property "on" > so the command line remains the same. > > For QEMU >= 2.5 is "off" by default and the bridge disappear, without > command line changes. If you were using "-M pc", and you expected "-device" to place things under the PCI-to-PCI bridge, that command line will not work anymore I think. Management tools can work around it. They can always set the new property to off---which by the way means it should not be "x" prefixed---and assume the PCI-to-PCI bridge is there if the property doesn't exist. But it's inconvenient, and we try to avoid lockstep changes to QEMU and management. Paolo >> Can we have two devices, on for a PCI expander bridge and one for a PCIe >> expander bridge? > > Gerd also asked for this, OK, I am going for it. > > Thanks, > Marcel > >> >> Paolo >> >