Re: Re: debugging Xen in a serial-less environment

[Jeremy Fitzhardinge <jeremy@goop.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