From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from eggs.gnu.org ([2001:4830:134:3::10]:47019) by lists.gnu.org with esmtp (Exim 4.71) (envelope-from ) id 1XmPm5-0000xL-N5 for qemu-devel@nongnu.org; Thu, 06 Nov 2014 11:19:11 -0500 Received: from Debian-exim by eggs.gnu.org with spam-scanned (Exim 4.71) (envelope-from ) id 1XmPlz-0006Wr-HC for qemu-devel@nongnu.org; Thu, 06 Nov 2014 11:19:05 -0500 Received: from mx1.redhat.com ([209.132.183.28]:45211) by eggs.gnu.org with esmtp (Exim 4.71) (envelope-from ) id 1XmPlz-0006Wn-7P for qemu-devel@nongnu.org; Thu, 06 Nov 2014 11:18:59 -0500 Date: Thu, 6 Nov 2014 17:18:41 +0100 From: Igor Mammedov Message-ID: <20141106171841.464a4f4f@nial.usersys.redhat.com> In-Reply-To: <545B9A7B.80101@redhat.com> References: <1414691045-4793-1-git-send-email-a.spyridakis@virtualopensystems.com> <20141030180216.GD31629@leverpostej> <545B1ACF.4090600@linaro.org> <545B9A7B.80101@redhat.com> MIME-Version: 1.0 Content-Type: text/plain; charset=US-ASCII 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: Paolo Bonzini Cc: Mark Rutland , Peter Maydell , "linaro-acpi@lists.linaro.org" , QEMU Developers , Hanjun Guo , "tech@virtualopensystems.com" 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? > 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. > > Paolo >