From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from eggs.gnu.org ([2001:4830:134:3::10]:48831) by lists.gnu.org with esmtp (Exim 4.71) (envelope-from ) id 1XmPuU-0005n7-P9 for qemu-devel@nongnu.org; Thu, 06 Nov 2014 11:27:52 -0500 Received: from Debian-exim by eggs.gnu.org with spam-scanned (Exim 4.71) (envelope-from ) id 1XmPuO-0000mt-Jf for qemu-devel@nongnu.org; Thu, 06 Nov 2014 11:27:46 -0500 Received: from mx1.redhat.com ([209.132.183.28]:57049) by eggs.gnu.org with esmtp (Exim 4.71) (envelope-from ) id 1XmPuO-0000mg-CK for qemu-devel@nongnu.org; Thu, 06 Nov 2014 11:27:40 -0500 Message-ID: <545BA16A.7030202@redhat.com> Date: Thu, 06 Nov 2014 17:27:22 +0100 From: Paolo Bonzini MIME-Version: 1.0 References: <1414691045-4793-1-git-send-email-a.spyridakis@virtualopensystems.com> <20141030180216.GD31629@leverpostej> <545B1ACF.4090600@linaro.org> <545B9A7B.80101@redhat.com> <20141106171841.464a4f4f@nial.usersys.redhat.com> In-Reply-To: <20141106171841.464a4f4f@nial.usersys.redhat.com> Content-Type: text/plain; charset=windows-1252 Content-Transfer-Encoding: 7bit Subject: Re: [Qemu-devel] [Linaro-acpi] [RFC PATCH 0/7] hw/arm/virt: Dynamic ACPI v5.1 table generation List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , To: Igor Mammedov Cc: Mark Rutland , Peter Maydell , "linaro-acpi@lists.linaro.org" , QEMU Developers , Hanjun Guo , "tech@virtualopensystems.com" On 06/11/2014 17:18, Igor Mammedov wrote: > On Thu, 06 Nov 2014 16:57:47 +0100 > Paolo Bonzini wrote: > >> On 06/11/2014 07:53, Hanjun Guo wrote: >>>> So the important question is _why_ the guest needs to see an ACPI >>>> environment. What exactly can ACPI provide to the guest that DT does not >>>> already provide, and why is that necessary? What infrastrucutre is >>>> needed for that use case? >>> >>> There is important feature called system device dynamic reconfiguration, >>> you know, hot-add/remove, if a gust need more/less memory or CPU, can we >>> add or remove them dynamically with DT? ACPI can do this, but I have no >>> idea if DT can. (Sorry, I don't know much about DT) >> >> Indeed hot-add/remove is the single biggest AML user in x86 QEMU. >> Whether you really need it, it depends on what you are adding/removing. >> >> For PCI there is no problem. We can use PCIe from the beginning, and >> use PCIe hotplug support that is already in QEMU. >> >> Memory and CPU are more problematic. For memory we could perhaps use a >> PCI memory device, though I'm not sure if that would require drivers in >> the OS or everything just works. > > BTW what's PCI memory device? Is there any reference I could read about it? Just something with a huge BAR. Like ivshmem, but teaching the OS to see it as memory. >> CPU hotplug, however, probably requires AML. Of course it can be >> generated in the firmware, like we used to do for x86, but Igor >> explained why it wasn't a great idea. That said, one of the problems >> ("never ending expansion of PV QEMU-BIOS interface") could be less >> important since ARM DT is a better interface than x86 fw_cfg. > Unfortunately we still would need to teach UEFI to recognize > QEMU specific DT entries that were just invented, > it doesn't matter what transport is used (DT or fw_cfg) to convey > new information to UEFI/BIOS. Right, it's just a bit more organized than fw_cfg. Paolo