Re: [Qemu-devel] [Xen-devel] [PATCH 3/3 v4] xenfb: Add [feature|request]-raw-pointer

[Paul Durrant <Paul.Durrant@citrix.com>]

> -----Original Message-----
> From: Gerd Hoffmann [mailto:kraxel@redhat.com]
> Sent: 12 October 2017 10:26
> To: Paul Durrant <Paul.Durrant@citrix.com>; 'Stefano Stabellini'
> <sstabellini@kernel.org>; Anthony Perard <anthony.perard@citrix.com>
> Cc: qemu-devel@nongnu.org; xen-devel@lists.xenproject.org; Owen Smith
> <owen.smith@citrix.com>
> Subject: Re: [Xen-devel] [PATCH 3/3 v4] xenfb: Add [feature|request]-raw-
> pointer
> 
>   Hi,
> 
> > It's probably OS specific though. I guess the behaviour changed
> > because the OS favours absolute pointing devices over relative ones
> > and how it has two absolute ones to choose from. How it reconciles
> > those, who knows?
> 
> Typically hid emulation calls qemu_input_handler_activate() when the
> guest initializes the device, which moves the device to the top of the
> priority list.
> 
> Visible effect on a typical guest with ps/2 mouse and usb-tablet is
> that qemu switches from relative mode (mouse) to absolute mode (tablet)
>  when the guest loads the usb hid driver.
> 
> I suspect pvmouse is doing the same thing.  So it may simply depend on
> guest driver load order whenever pvmouse or usb-tablet is used.
> 
> Simplest fix is probably to only attach the device you plan to use to
> the guest.  If you can't turn off pvmouse for xen guests then you might
> want drop the qemu_input_handler_activate() call, so it behaves simliar
> to the ps/2 mouse (is used in case no other pointer device is present).

Avoiding the activate call sounds reasonable and should avoid the behavioural change.

Cheers,

  Paul

> 
> HTH,
>   Gerd