[PATCH libinput] udev: add quirk for Chalkboard Electronics HID Touchscreen

[Matt Porter]

On Wed, Sep 20, 2017 at 10:14:41AM +1000, Peter Hutterer wrote:
> Hi Matt,

Hi Peter!

> On Tue, Sep 19, 2017 at 12:41:52PM -0400, Matt Porter wrote:
> > The Chalkboard Electronics HID Touchscreen is classified as
> > a tablet device by systemd udev because it has BTN_TOOL_PEN
> > support. It also reports a resolution of 0 for both X and Y
> > axes in absinfo. This causes libinput to reject it as an
> > invalid tablet device.
> > 
> > This quirk reclassifies the device as a touchscreen which
> > allows it to be added as a valid input device.
> > 
> > Signed-off-by: Matt Porter <mporter at konsulko.com>
> > ---
> >  udev/90-libinput-model-quirks.hwdb | 7 +++++++
> >  1 file changed, 7 insertions(+)
> > 
> > diff --git a/udev/90-libinput-model-quirks.hwdb b/udev/90-libinput-model-quirks.hwdb
> > index 72fcdca..6348f0c 100644
> > --- a/udev/90-libinput-model-quirks.hwdb
> > +++ b/udev/90-libinput-model-quirks.hwdb
> > @@ -72,6 +72,13 @@ libinput:name:*ETPS/2 Elantech Touchpad*:dmi:*svnASUSTeKCOMPUTERINC.:pnX555LAB:*
> >   LIBINPUT_MODEL_TOUCHPAD_VISIBLE_MARKER=1
> >  
> >  ##########################################
> > +# Chalkboard Electronics
> > +##########################################
> > +libinput:name:Chalkboard Electronics HID Touchscreen:dmi:*
> > + ID_INPUT_TABLET=0
> > + ID_INPUT_TOUCHSCREEN=1

First off, thanks for the very good explanation of where this quirk
handling should live...I wasn't entirely clear on the separation from my
read of systemd and libinput.

> There are three things we have to fix here:
> 1) ID_INPUT_* is not something set by libinput so if it is wrong, we should fix
> it at the source (i.e. systemd) so it will be correct for everyone. By the
> time libinput sees this device, the ID_INPUT_* must be correct already, that
> is one of the requirements we have from the base system.

Ok. Since systemd's logic of normally classifying anything with a pen
tool as a tablet makes sense, tt appears I'll want to add something
similar to 65-libwacom.rules. We definitely are a traditional
touchscreen device and not something with semantics like a Wacom
tablet. Something like:

65-chalkboard-electronics.rules
-------------------------------
# udev rules for Chalkboard Electronics devices

ACTION!="add|change", GOTO="chalkboard_end"
KERNEL!="event[0-9]*", GOTO="chalkboard_end"

ENV{ID_BUS}=="usb", ENV{ID_VENDOR_ID}=="04d8", ENV{ID_MODEL_ID}=="f723", ENV{ID_INPUT}="1", ENV{ID_INPUT_TABLET}="", ENV{ID_INPUT_TOUCHSCREEN}="1"

LABEL="chalkboard_end"

> 2) The absinfo bits can be set with the EV_ABS_.. in 60-evdev.hwdb. Have a
> look at that file, it includes the explanation on how to set it.

Ok, perfect. I totally missed this and I have a patch I'll send upstream
to systemd.

> 3) The libinput part of this will be to add a
> LIBINPUT_MODEL_CHALKBOARD_ELECTRONICS_TOUCHSCREEN tag for this particular
> model. That needs to be parsed in evdev_pre_configure_model_quirks because
> we need to libevdev_disable_event_code(BTN_TOOL_PEN) for that to make sure
> the rest of libinput has the data it expects.

I see, ok. Is this necessary even if the device is detected as a
touchscreen? It appears that BTN_TOOL_PEN events are only used in the
evdev-tablet.c paths so I would have thought it unncessary to disable
pen events. That is, assuming I have the first two cases above
implemented. Is this simply for correctness and to not have bogus pen
events arriving at get_key_type()? In any case, I can rework as
described above.

Thanks,
Matt