Re: [PATCH] usb/hcd-ehci: Fix error handling on missing device for iTD

[Gerd Hoffmann]

On Wed, Oct 14, 2020 at 11:41:06AM +0100, Anthony PERARD wrote:
> The EHCI Host Controller emulation attempt to locate the device
> associated with a periodic isochronous transfer description (iTD) and
> when this fail the host controller is reset.
> 
> But according the EHCI spec 1.0 section 5.15.2.4 Host System
> Error, the host controller is supposed to reset itself only when it
> failed to communicate with the Host (Operating System), like when
> there's an error on the PCI bus. If a transaction fails, there's
> nothing in the spec that say to reset the host controller.
> 
> This patch rework the error path so that the host controller can keep
> working when the OS setup a bogus transaction, it also revert to the
> behavior of the EHCI emulation to before commits:
> e94682f1fe ("ehci: check device is not NULL before calling usb_ep_get()")
> 7011baece2 ("usb: remove unnecessary NULL device check from usb_ep_get()")
> 
> The issue has been found while trying to passthrough a USB device to a
> Windows Server 2012 Xen guest via "usb-ehci", which prevent the USB
> device from working in Windows. ("usb-ehci" alone works, windows only
> setup this weird periodic iTD to device 127 endpoint 15 when the USB
> device is passthrough.)
> 
> Signed-off-by: Anthony PERARD <anthony.perard@citrix.com>

Added to usb queue.

thanks,
  Gerd