[PATCH]: mtdev could be disabled at configuration

[Pekka Paalanen]

On Tue, 11 Jun 2013 09:01:48 +0200
Benjamin Tissoires <benjamin.tissoires at gmail.com> wrote:

> On Mon, Jun 10, 2013 at 8:42 AM, Pekka Paalanen <ppaalanen at gmail.com> wrote:
> > On Fri, 7 Jun 2013 12:11:14 +0200
> > Marc Chalain <marc.chalain at gmail.com> wrote:
> >
> >> mtdev is not necessary on some device (desktop or set-top-box). For
> >> embedded solution the minimum of dependencies is required. "configure"
> >> accepts the --disable-mtdev option.
> >
> > Hi Marc,
> >
> > with this patch, if weston is compiled with --disable-mtdev, it looks
> > like it will still happily open multitouch devices, expose them to
> > Wayland clients, and feed them garbage or fail or whatever. Right?
> 
> Hi Pekka,
> 
> no. mtdev is a compatibility layer for converting very rare
> touchscreen using the multitouch protocol A into the mostly used
> multitouch protocol B.
> To my mind, only legacy devices (ntrig 0001 and few others) use the protocol A.
> So without mtdev, wayland will open and handle most of the multitouch
> screen happily.
> 
> >
> > I think the proper approach is to change the configure option into
> > --disable-multitouch or --disable-touchscreen, which would not only
> > drop the dependency to mtdev, but also make Weston ignore all
> > touchscreen devices since it will not be able to handle them.
> 
> Without mtdev, wayland should only ignore multitouch screen not
> presenting the ABS_MT_SLOT axis.
> Those relying on SYN_MT_REPORT do not provide tracking (which is done by mtdev).
> 
> So my guess is that if you detect multitouch screens by looking at
> ABS_MT_SLOT, then everything will be fine whether or not you have
> mtdev:
> - multitouch B screens will correctly be handled
> - multitouch A screens will be processed as a single touch screen,
> which is not a problem because the kernel provides single touch
> emulation since the early days of multitouch. And if mtdev is present,
> then it will show the ABS_MT_SLOT axis, leading to the previous case.
> 
> Bonus point, mtdev has not been updated since a long time, and is
> missing the bits allowing you to retrieve the initial per-slot states.
> And you may find useful to retrieve the current states when weston
> launches.

Thank you for clarifying that, Benjamin.

Does this mean that we need explicit single-touch support in Weston?

I don't think we have that yet. Everything touchy goes through mtdev,
which makes also real single-touch devices look like multitouch devices
except they never report more than one contact. Do I understand that
right?

Marc, in any case, I think you should check that Weston correctly
ignores touch devices it cannot support without mtdev, as per
Benjamin's instructions above.

Retrieving current state is a matter for another time.


Thanks,
pq