From mboxrd@z Thu Jan 1 00:00:00 1970 From: Ian Jackson Subject: Re: [PATCH V6 3/7] libxl: add pvusb API Date: Fri, 11 Sep 2015 16:42:15 +0100 Message-ID: <22002.63063.974633.501641@mariner.uk.xensource.com> References: <1439202928-24813-1-git-send-email-cyliu@suse.com> <1439202928-24813-4-git-send-email-cyliu@suse.com> <1441721852.24450.120.camel@citrix.com> <55F2F64F02000066000508CA@relay2.provo.novell.com> <1441978018.3549.33.camel@citrix.com> <55F2DD66.1040507@suse.com> <1441980590.3549.46.camel@citrix.com> <55F2E29D.10805@suse.com> <1441982504.3549.69.camel@citrix.com> Mime-Version: 1.0 Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: 7bit Return-path: In-Reply-To: <1441982504.3549.69.camel@citrix.com> List-Unsubscribe: , List-Post: List-Help: List-Subscribe: , Sender: xen-devel-bounces@lists.xen.org Errors-To: xen-devel-bounces@lists.xen.org To: Ian Campbell Cc: Juergen Gross , wei.liu2@citrix.com, george.dunlap@eu.citrix.com, Ian.Jackson@eu.citrix.com, Chun Yan Liu , xen-devel@lists.xen.org, Jim Fehlig , Simon Cao List-Id: xen-devel@lists.xenproject.org Most of what you say is right, I think, but: Ian Campbell writes ("Re: [Xen-devel] [PATCH V6 3/7] libxl: add pvusb API"): > On Fri, 2015-09-11 at 16:18 +0200, Juergen Gross wrote: > > In theory I think up to 7 cascaded > > hubs are possible, but I don't think the resulting theoretical maximum > > of about 1 trillion devices on a bus is to be considered. :-) > > And this suggests that in principal a Linux hostbus could be 5*7 bits == 35 > bits, maybe. Or at least that any USB address can be encoded in that many > bits. No. The total possible number of `buses' in that sense per root is: 1 root + 31 in theory a hub plugged into each of 31 ports + 31^2 in theory a hub plugged into each port ... + 31^6 You could plug hubs into the last layer but the maximum depth is 7 so you wouldn't be able to plug any devices into that last hub. And of course the number of root hubs is not really limited by anything meaningful. Ian.