qemu & xhci mini howto (was: Re: [Qemu-devel] [ANNOUNCE] qemu-kvm-1.1-rc3)

[Gerd Hoffmann <kraxel@redhat.com>]

On 05/28/12 11:30, Avi Kivity wrote:
> On 05/25/2012 11:36 AM, Veruca Salt wrote:
>>
>> Avi- would love to test out 1.1, as we are currently using the ehci method
>>  which has been frozen at 'experimental' for so long.
>>
>> Is there any user documentation on the xhci methods?
> 
> Copying qemu-devel, where someone may know the answer.

There are no docs.  But xhci can handle all devices by itself, no need
to do all this companion controller stuff you have to do with ehci for
usb 1.1 compatibility.  Thus it's pretty simple actually:


(1) You add the xhci host adapter:

    qemu $args -device nec-usb-xhci,id=xhci

(2) You add usb devices devices as usual:

    qemu $args -device usb-tablet,bus=xhci.0

(3) There is no third step ;)


Advantages of xhci:
 * higher performance, less cpu overhead (thanks to the
   virtualization/emulation friendly hardware design).

Known issues (for qemu 1.1, list hopefully becomes shorter for 1.2):
 * Got less testing than ehci.
 * No usb-hub support yet (i.e. you are limited to the 4 root ports,
   but as the qemu-emulated usb hub supports usb 1.1 only you probably
   want avoid it anyway ...).
 * No usb 3.0 ports yet.
 * No isochronous transfer support yet.
 * No seabios support yet (i.e. you can't boot from xhci-connected
   usbsticks).

cheers,
  Gerd