Debugging tablet issues

Required tablet capabilities

To handle a tablet correctly, libinput requires a set of capabilities on the device. When these capabilities are missing, libinput ignores the device and prints an error to the log. This error messages reads

missing tablet capabilities: xy pen btn-stylus resolution. Ignoring this device.

or in older versions of libinput simply:

libinput bug: device does not meet tablet criteria. Ignoring this device.

When a tablet is rejected, it is usually possible to verify the issue with the libinput record tool.

  • xy indicates that the tablet is missing the ABS_X and/or ABS_Y axis. This indicates that the device is mislabelled and the udev tag ID_INPUT_TABLET is applied to a device that is not a tablet. A bug should be filed against systemd.
  • pen or btn-stylus indicates that the tablet does not have the BTN_TOOL_PEN or BTN_STYLUS bit set. libinput requires either or both of them to be present. This indicates a bug in the kernel driver or the HID descriptors of the device.
  • resolution indicates that the device does not have a resolution set for the x and y axes. This can be fixed with a hwdb entry, locate and read the 60-evdev.hwdb file on your machine and file a pull request with the fixes against systemd.