Archipelago » qemu

More USB tips & tricks

======================

Recently the usb pass through driver (also known as usb-host) and the

qemu usb subsystem gained a few capabilities which are available only

via qdev properties, i,e. when using '-device'.

physical port addressing

------------------------

First you can (for all usb devices) specify the physical port where

the device will show up in the guest.  This can be done using the

"port" property.  UHCI has two root ports (1,2).  EHCI has four root

ports (1-4), the emulated (1.1) USB hub has eight ports.

Plugging a tablet into UHCI port 1 works like this:

        -device usb-tablet,bus=usb.0,port=1

Plugging a hub into UHCI port 2 works like this:

        -device usb-hub,bus=usb.0,port=2

Plugging a virtual usb stick into port 4 of the hub just plugged works

this way:

        -device usb-storage,bus=usb.0,port=2.4,drive=...

You can do basically the same in the monitor using the device_add

command.  If you want to unplug devices too you should specify some

unique id which you can use to refer to the device ...

        (qemu) device_add usb-tablet,bus=usb.0,port=1,id=my-tablet

        (qemu) device_del my-tablet

... when unplugging it with device_del.

USB pass through hints

----------------------

The usb-host driver has a bunch of properties to specify the device

which should be passed to the guest:

  hostbus=<nr> -- Specifies the bus number the device must be attached

  to.

  hostaddr=<nr> -- Specifies the device address the device got

  assigned by the guest os.

  hostport=<str> -- Specifies the physical port the device is attached

  to.

  vendorid=<hexnr> -- Specifies the vendor ID of the device.

  productid=<hexnr> -- Specifies the product ID of the device.

In theory you can combine all these properties as you like.  In

practice only a few combinations are useful:

  (1) vendorid+productid -- match for a specific device, pass it to

      the guest when it shows up somewhere in the host.

  (2) hostbus+hostport -- match for a specific physical port in the

      host, any device which is plugged in there gets passed to the

      guest.

  (3) hostbus+hostaddr -- most useful for ad-hoc pass through as the

      hostaddr isn't stable, the next time you plug in the device it

      gets a new one ...

Note that USB 1.1 devices are handled by UHCI/OHCI and USB 2.0 by

EHCI.  That means a device plugged into the very same physical port

may show up on different busses depending on the speed.  The port I'm

using for testing is bus 1 + port 1 for 2.0 devices and bus 3 + port 1

for 1.1 devices.  Passing through any device plugged into that port

and also assign them to the correct bus can be done this way:

    qemu -M pc ${otheroptions}                           \

        -usb                                             \

        -device usb-ehci,id=ehci                         \

        -device usb-host,bus=usb.0,hostbus=3,hostport=1  \

        -device usb-host,bus=ehci.0,hostbus=1,hostport=1