vmmouse kernel driver

[Hans de Goede]

Hi,

On 09/26/2014 09:06 AM, Thomas Hellstrom wrote:
> Hi!
> 
> On 09/26/2014 03:36 AM, Peter Hutterer wrote:
>> On Wed, Sep 24, 2014 at 11:12:50AM +0200, Thomas Hellstrom wrote:
>>> While looking at a vmmouse kernel driver, I wonder how the Xorg evdev
>>> driver can be configured to receive both absolute and relative events
>>> from the same device as the vmmouse sometimes sends absolute events and
>>> sometimes relative. Is the "IgnoreAbsoluteAxes" "False" option sufficient?
>> at the same time, or depending on the configuration? The
>> IgnoreAbsoluteAxes/IgnoreRelativeAxes options simply disable one of the two
>> on startup, allowing the other one to be initialized. that's for virtual
>> devices mostly used in VMs because our device autodetection fails there.
>>
>> So short answer: yes, should be sufficient provided you stay in that mode
>> for the lifetime of the device.
> 
> Thanks for the answer. The problem is we don't. We could suddenly decide
> that apparently somebody applied a screen tranformation or is running a
> game and revert back to relative events.
> Otherwise the preferred choice is absolute events for minimal cursor
> latency.
> 
> I know that for this reason the virtual USB mice are duplicated: one for
> absolute events and one for relative events but I haven't looked to
> closely at what level this actually happens.
> 
> But whatever solution that emerges needs to work also with the new
> compositors. I guess I have to look at somehow make the mouse appear as
> two different ps2 mice from within the kernel driver...

Actually one ps/2 device(mouse) which registers 2 input devices, that is
more or less quite normal for trackpoint / touchpad combo's which are
interfaced over a single ps/2 connection (some use ps/2 multiplexing, but
others both touchpad and trackpoint ps/2 packets are send over the same
ps/2 device).

See drivers/input/mouse/alps.c for an example of this, search for "dev2"
to all the code dealing with the second device. This way you can simply
register both an absolute and a relative device, and send events out of
the right one depending on the mode. That is probably the best way to deal
with this.

Regards,

Hans