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

[Hans de Goede]

Hi,

On 21-09-17 16:00, Matt Porter wrote:
> On Thu, Sep 21, 2017 at 10:59:08AM +0200, Hans de Goede wrote:
>> Hi,
>>
>> On 19-09-17 18:41, 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>
>>
>> Have you considered adding special handling for this device
>> to the kernel's hid drivers ? The hid subsys has sub drivers
>> for device specific handling and if the device never actually
>> has a pen, then the right fix would be to not make the kernel
>> export this. Note I assume this is for a so called
>> "smart" whiteboard for in classes ? If that is the case then
>> the device may actually have a pen/stylus like device in
>> some configuration. Some of these smart boards have what
>> are basically empty whiteboard-marker in multiple colors
>> and the device may report these as different styluses ...
> 
> I hadn't really considered that since this userspace fixup
> basically follows the pattern I see for other devices in
> systemd's hwdb.

In this case (exporting a wrong event capability) a kernel fix
seems more appropriate to me. In general we try to fix things
as early in the chain as possible. hwdb quirks are more for
things like: Yes this device supports semi-mt and the kernel
exports that info, but the semi-mt coordinates are so unreliable
that we really should just treat it as a single touch device.

Anyways this is just my 2 cents, Peter what do you think,
kernel fix or hwdb ?

> Just to clarify, these are not "smartboard"
> style devices. They are typical 7-14" touchscreen displays
> with HDMI/USB interface from https://www.chalk-elec.com/

Ok, that is good to know, really weird the export a
BTN_TOOL_PEN then.

Regards,

Habs


> 
> The updated patch for this is at
> https://github.com/systemd/systemd/pull/6880 based on Peter's
> earlier comments. It could be solved in the kernel as you
> suggest, however it appears that usually that approach is for
> very different hid devices with custom protocols (e.g.
> logitech-hidpp). I could suppress the pen tool and update absinfo
> in a hid-chalkboard.c if that's preferred. There could be an
> advantage here for those that aren't using systemd udev.
> 
> -Matt
>