The DELL XPS13 (2015) still has some issues when using Ubuntu 14.04 LTS. Most of the issues can be resolved by installing a Linux kernel of the 4.x-line. However, switching the enabled status of the touchpad is still finicky. Since I use a mouse most of the time when working with the machine, I'd like to deactivate / activate the touchpad in a convenient way.
For that matter, I wrote a small BASH script that allows me to toggle the enabled status of the touchpad. The BASH script uses xinput to read the current status of the touchpad and sets it to enabled / disabled as appropriate.
I got most of the information for fixing the issues with Ubuntu 14.04 LTS and the DELL XPS13 (2015) from this blog post which goes into great detail on how to configure the system properly.
The DELL XPS13 (2015) touchpad can operate via PS2 or I2C. In my case, both operation modes showed an entry via xinput. This seems to cause another problem: If you use the Ubuntu System Tools to manually deactivate the touchpad, it will switch right back to the enabled state once you disabled it. To fix this behavior, you have to blacklist the PS2 operation mode, which can be done as follows.
Use xinput to get some information on the touchpad.
$ xinput
This should yield something like this:
Virtual core pointer id=2 [master pointer (3)]
↳ Virtual core XTEST pointer id=4 [slave pointer (2)]
↳ DLL0665:01 06CB:76AD UNKNOWN id=14 [slave pointer (2)]
If there is no mouse connected to the system, these two entries should be the only ones showing under "Virtual core pointer". If you notice something like "PS2 touchpad", then the PS2 operation is still active. To blacklist the PS2 operation mode, add the line blacklist psmouse to /etc/modprobe.d/blacklist.conf.
$ echo -e "\nblacklist psmouse" | sudo tee -a /etc/modprobe.d/blacklist.conf
$ sudo update-initramfs -u
Reboot the system and check the status using xinput again. It should look like the example above.
The script reads the device ID of the virtual core pointer associated with the touchpad in I2C mode. To extract the necessary information from xinput, the script needs to identify the correct device. On my machine, the device name is DLL0665:01 06CB:76AD UNKNOWN. The script specifically looks for this device name within the output of xinput, so if this is different on your machine for whatever reason, you need to adjust the variable $TOUCHPAD_DEVICE_PATTERN to your needs.
The script does not preserve the last enabled status between system reboots.
Calling the script without additional parameters toggles the enabled status.
$ touchpad-activator
Calling the script with the parameter off disables the touchpad.
$ touchpad-activator off
Calling the script with the parameter on enables the touchpad.
$ touchpad-activator on
Calling the script with the parameter status shows the associated device ID and the current enabled status.
$ touchpad-activator status
This yields
Touchpad Device ID: 14
Touchpad Status : Off
The script creates the directory /home/$USER/.touchpad-activator and logs its activity and errors to the file /home/$USER/.touchpad-activator/touchpad-activator.log.
This script is released under the MIT license.