From mboxrd@z Thu Jan 1 00:00:00 1970 From: Christopher Covington Subject: Re: what should a virtio-mmio transport without a backend look like? Date: Thu, 20 Jun 2013 08:58:03 -0400 Message-ID: <51C2FC5B.7080406@codeaurora.org> References: <1371726501.3231.22.camel@hornet> Mime-Version: 1.0 Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: 7bit Return-path: In-Reply-To: <1371726501.3231.22.camel@hornet> List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Sender: virtualization-bounces@lists.linux-foundation.org Errors-To: virtualization-bounces@lists.linux-foundation.org To: Peter Maydell Cc: =?UTF-8?B?S09OUkFEIEZyw6lkw6ly?= =?UTF-8?B?aWM=?= , Pawel Moll , virtualization@lists.linux-foundation.org List-Id: virtualization@lists.linuxfoundation.org Hi Peter, On 06/20/2013 07:08 AM, Pawel Moll wrote: > On Thu, 2013-06-20 at 11:29 +0100, Peter Maydell wrote: >> I'm (finally) trying to add virtio-mmio support properly to >> QEMU now Fred has put all the refactoring foundations in place. >> >> 1. One question I've run into is: what should a virtio-mmio transport >> with no backend look like to the guest OS? The spec as written >> seems to assume that there's always some backend present. >> (The idea is that QEMU might just always instantiate say 8 >> mmio transports, and then whether they actually have a >> blk/net/whatever backend depends on user options). >> >> It looks as if the current linux driver insists (if it sees a >> device tree node) that the MagicValue register at least is >> correct (otherwise it complains). So one possibility would >> be "MagicValue/Version/VendorID must read as usual, DeviceID >> should read as some special "nothing here" value (0?), everything >> else can RAZ/WI". Might it be reasonably easy to just not enumerate unused transports in the device tree or kernel parameters? Regards, Christopher -- Employee of Qualcomm Innovation Center, Inc. Qualcomm Innovation Center, Inc. is a member of Code Aurora Forum, hosted by the Linux Foundation.