From mboxrd@z Thu Jan 1 00:00:00 1970 From: Jeremy Fitzhardinge Subject: Re: Re: debugging Xen in a serial-less environment Date: Sat, 07 Mar 2009 01:48:49 -0800 Message-ID: <49B24301.6020609@goop.org> References: <49AF9E92.5060207@redhat.com> <49B17A8C.90706@goop.org> Mime-Version: 1.0 Content-Type: text/plain; charset=ISO-8859-15; format=flowed Content-Transfer-Encoding: 7bit Return-path: In-Reply-To: List-Unsubscribe: , List-Post: List-Help: List-Subscribe: , Sender: xen-devel-bounces@lists.xensource.com Errors-To: xen-devel-bounces@lists.xensource.com To: Christian Tramnitz Cc: xen-devel@lists.xensource.com List-Id: xen-devel@lists.xenproject.org Christian Tramnitz wrote: > But it seems to be a bit harder to find those dongles. It look like > the only model (NET20DC) isn't RoHS compliant which explains why I > don't find a place to order them in Eruope. > But other than that this seems to be a good long-term alternative to a > serial console. I haven't looked at the code for it in the linux > kernel but does anyone know if it's required to get all the hcd and > usbcore stuff loaded before being able to use the debug port? If not, > whats the behaviour of the usb bus (and the debug port) when those > drivers are loaded by dom0 subsequently? It appears that the USB hardware has a special simplified PIO programming mode that is relatively easy to operate without the full USB stack in place. But there's a comment in the Linux code to the effect that you can't keep a debug port early console because the full USB stack will subsequently reset and take over the hardware. In Xen I'm guessing that means that you'd have to dedicate a USB controller to debug output and prevent dom0 from using it. Which seems a bit inconvenient. J