[Qemu-devel] Re: USB-OHCI / UHCI: Isochronous transfer not working on Linux host

[Max Krasnyansky <maxk@kernel.org>]

Sorry for delay in replying.
(CCing Mark Burkley who recently posted EHCI patches)

Thomas Bandelier wrote:
> Hi Arnon, Max, Pierre,
> 
> Arnon, Thanks for your feedback on this point.
> 
> As we need to manage several USB 2.0 devices in our environment, we are 
> going to work on this aspect. We are very motivated to make it work.
> 
> Do you (Max and/or Arnon) have any idea of what should be done / 
> reworked in order to support USB 2.0 devices and especially isochronous 
> transfers in QEMU?
Most USB 2.0 devices should work just fine with the current UHCI code. 
Including isochronous transfers. While developing new UHCI 
implementation I was testing it with several 2.0 devices like USB 
storage devices and MS Webcam. Webcam uses isoc transfers and worked 
fairly well.
However since UHCI does not do 2.0 rates USB bandwidth is much lower in 
the guest.

> We would prefer keeping OHCI implementation, but do you think we should 
> switch to UHCI? Or maybe EHCI?
> 
> If we can keep OHCI, what should we begin to do in order to debug 
> current QEMU OHCI implementation? Same question for the other 
> controllers if we have to switch.
Ideally we need to switch to EHCI in order to support high USB2.0 
speeds. Not too long ago Mark posted a EHCI implementation (I have not 
had much luck with it and XP yet though).
Otherwise if you're ok with lower BW then UHCI should work fine.

Max