From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from eggs.gnu.org ([2001:4830:134:3::10]:46431) by lists.gnu.org with esmtp (Exim 4.71) (envelope-from ) id 1b2ZWt-000616-2L for qemu-devel@nongnu.org; Tue, 17 May 2016 03:35:00 -0400 Received: from Debian-exim by eggs.gnu.org with spam-scanned (Exim 4.71) (envelope-from ) id 1b2ZWp-0003S2-09 for qemu-devel@nongnu.org; Tue, 17 May 2016 03:34:58 -0400 Received: from [59.151.112.132] (port=17761 helo=heian.cn.fujitsu.com) by eggs.gnu.org with esmtp (Exim 4.71) (envelope-from ) id 1b2ZWo-0003Ra-8e for qemu-devel@nongnu.org; Tue, 17 May 2016 03:34:54 -0400 References: <1462508442-9407-1-git-send-email-caoj.fnst@cn.fujitsu.com> <1462508442-9407-10-git-send-email-caoj.fnst@cn.fujitsu.com> <573878E7.7070807@redhat.com> From: Cao jin Message-ID: <573ACAA2.1040107@cn.fujitsu.com> Date: Tue, 17 May 2016 15:39:14 +0800 MIME-Version: 1.0 In-Reply-To: <573878E7.7070807@redhat.com> Content-Type: text/plain; charset="windows-1252"; format=flowed Content-Transfer-Encoding: 7bit Subject: Re: [Qemu-devel] [PATCH v5 09/11] pci bridge dev: change msi property type List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , To: Marcel Apfelbaum , qemu-devel@nongnu.org Cc: "Michael S. Tsirkin" , Markus Armbruster On 05/15/2016 09:25 PM, Marcel Apfelbaum wrote: > On 05/06/2016 07:20 AM, Cao jin wrote: >> From bit to enum OnOffAuto. >> >> cc: Michael S. Tsirkin >> cc: Markus Armbruster >> cc: Marcel Apfelbaum >> Signed-off-by: Cao jin >> --- >> >> Actually, I am not quite sure this device need this change, RFC. >> > > Well, it already has the 'msi' property, so we may want to make it > standard 'OnOffAuto'. > One problem I can see is the change of semantics. Until now msi=on means > 'auto'. From now on > it means 'force msi=on', fail otherwise. If I got this right, old > machines having msi=on > will failed to start on platforms with msibroken=true, right? Exactly, and patch 11 indeed has semantics change. According to what we discussed before: "if user want msi=on explicitly on command line, then msi_init`s failure should result in failing to create device", this semantics change seems can`t be avoid. > Maybe we should preserve the semantics for old machines? (this patch > does not actually > affect the semantics, but patch 11/11 should, otherwise why change it to > OnOffAuto, right? ) IMHO, in this case, keep compat maybe a burden on us, and make command-line confusing. See my understanding: before: command line format is msi=on/off, and 'on' means auto now: we change command line to msi=on/off/auto, and keep compat is meaning 'on' still means auto? If so, why need 'auto' So, I am thinking, maybe we can help old machine user update their configuration, I mean: when they set msi=on on platforms with msibroken=true, they definitely fail, so we should give a clear hint in error message to help them know what should do to start the machine, like "please use msi=auto and try again" -- Yours Sincerely, Cao jin