"disable touchpad while typing" doesn't work on xps 13 and some other laptop

Owning a XPS13 myself I have experienced this issue "first hand" and can confirm from making the change myself over the last 24 hours that the improvement is very noticeable.

Previously when typing the cursor would jump all over the place (mainly to the bottom left) and open up other windows, so much so I switched off the touch pad.

Now having carried out the change I have not experienced this and am currently working with the touch pad switched back on with no issues to report.

To clarify, I carried out the package install and didn't carry out the modification*

This is indeed a quite annoying bug. I've disabled the touchpad on my Dell XPS 13 9360 because it is way too sensitive and registering false clicks.

I'm using 16.04 LTS.

So how might one fix the issue? Can I simply add those conf settings, or is it a combination of the settings changes and package install?

That package is currently not installed on my system. I do have xserver-xorg-input-synaptics-hwe-16.04 installed...

/usr/share/X11/xorg.conf.d/50-synaptics.conf has this:

# Example xorg.conf.d snippet that assigns the touchpad driver
# to all touchpads. See xorg.conf.d(5) for more information on
# InputClass.
# DO NOT EDIT THIS FILE, your distribution will likely overwrite
# it when updating. Copy (and rename) this file into
# /etc/X11/xorg.conf.d first.
# Additional options may be added in the form of
# Option "OptionName" "value"
#
Section "InputClass"
        Identifier "touchpad catchall"
        Driver "synaptics"
        MatchIsTouchpad "on"
# This option is recommend on all Linux systems using evdev, but cannot be
# enabled by default. See the following link for details:
# http://who-t.blogspot.com/2010/11/how-to-ignore-configuration-errors.html
      MatchDevicePath "/dev/input/event*"
EndSection

I simply added:

        Option "Tapping" "on"
        Option "PalmDetection" "on"

I also enabled "Disable touchpad while typing" under "Mouse and Touchpad" in System Settings...Probably did the same thing as adding those lines in the file. The touchpad behaved much better after that.

I built a xserver-xorg-input-synaptics package for improving the user experience of the touchpad.

On xenial, you can test this experimental package by flowing command:
$ sudo add-apt-repository ppa:lihow731/xenial
$ sudo apt-get update
$ sudo apt-get install xserver-xorg-input-synaptics=1.8.2-1ubuntu3somerville1

More detail:
My modification is "ignore the BTN_TOOL_FINGER event".
On synaptic touchpad, the BTN_TOOL_FINGER event will be sent out at end of serial touch events.
The xserver-xorg-input-synaptics will process the BTN_TOOL_FINGER event as "one finger touched" (in my experiment, it look like a "click" sent out).

The current windows will lost focus when other window be clicked by the BTN_TOOL_FINGER event.
We don't expect this click action.
This behavior will cause users have bad user experiment.

Again, this is a experimental package.
Because, I don't know what is the BTN_TOOL_FINGER event.
And, is it appropriate to ignore this event?
Or, is this BTN_TOOL_FINGER event used by some gestures?
Another thing, I don't find the BTN_TOOL_FINGER event be handled in libinput source code.

The attached file is the patch to ignore the BTN_TOOL_FINGER.

I tried the solution in the comment #4.
I feel it is not good enough.
I often lost my windows focus when my palm touched the touchpad.

More information about the BTN_TOOL_FINGER event.
I found the BTN_TOOL_FINGER definition in https://www.kernel.org/doc/Documentation/input/event-codes.txt.

There are four events: BTN_TOOL_FINGER, BTN_TOOL_DOUBLETAP, BTN_TOOL_TRIPLETAP, BTN_TOOL_QUADTAP.
One of these events will be sent when click down and click up.
Only one finger touched the touchpad, the BTN_TOOL_FINGER is sent.
Two fingers touched, the BTN_TOOL_DOUBLETAP is sent.
Three fingers touched, the BTN_TOOL_TRIPLETAP is sent.
Four fingers touched, the BTN_TOOL_QUADTAP is sent.

In the xserver-xorg-input-synaptics, the driver knows how many finger is touching via these events.

In the source code, the number of the touching finger is saved in hw->numFingers.
And, the "numFingers == 1" only be used in "Two finger emulation".

Current investigation state:
The behavior of the BTN_TOOL_FINGER is correct. We should not ignore this event.

As Spike mention in comment #3, this issue is cause by the "tap as click".
The experience will be better when we uncheck the "tap as click" in the Mouse & Touchpad settings.

If you want the "tap as click" function and a good touchpad experience.
I am surveying how to solve this situation.

I try to have good touchpad experience when enable "tap to click".
Here is my properties that I feel the touchpad would not annoy me when I typping.

In xinput:
Synaptics Tap Time: 60

In syndaemon:
PalmDetect = 0
PalmMinWidth = 7
ref: https://wiki.archlinux.org/index.php/Touchpad_Synaptics#Disable_touchpad_while_typing

More detail:
1. Synaptics Tap Time:
 The default value is 180.
 The "tap to click" is too sensitive.
 My tap time around 0.04 ~ 0.08 second.
 So, I set it to 60 (0.06 second).
 The side effect is the "tap to click" will lost function when the tap time longer than 0.06 second.

2. The syndaemon settings:
PalmDetect = 1
PalmMinWidth = 10
On XPS13, the touchpad won't sent out the z (pressure) value.
When I set the PalmMinWidth = 7. I feel the "tap to click" is seldom to be emit.
But, actually, I don't know if this is the effect of this value.
TODO: I need to print some debug log to debug.

Below is my conclusion after surveying the palm detect function on XPS13 9360.
The palm detect function is a hardware limitation in xserver-xorg-input-synaptic in XPS13 9360.
 The touchpad does not support "pressure" and "finger width" information.
 These two values are important information in palm detect function.
 Palm detect function would not detect a palm precisely without these values.
 In Xorg.0.log:
[ 7.688] (--) synaptics: DLL075B:01 06CB:76AF Touchpad: invalid pressure range. defaulting to 0 - 255
[ 7.688] (--) synaptics: DLL075B:01 06CB:76AF Touchpad: invalid finger width range. defaulting to 0 - 15

About the "Disable touchpad while typing" option, I don't know why this option is removed in Xenial.

Another solution: disable the "tap to click" while typing.
On Xenial, this function should be enabled automatically.
But, when the machine have two touchpad devices, this function will fail.

I built a debian package to disable the "SynPS/2 Synaptics TouchPad" and make the "disable the tap to click while typing" function work.

$ sudo add-apt-repository ppa:lihow731/xenial
$ sudo apt-get update
$ sudo apt-get install oem-workaround-touchpad-block-synps2
Then, re-login Xserver.

For more detail, please refer below link:
https://ubuntuforums.org/showthread.php?t=2316240

More information:
The two touchpad input devices causes the "disable 'tap to click' while typing" function fail.
During booting, the psmouse will register a PS/2 touchpad input device and the hid-multitouch will register another i2c touchpad input device.

After booted, we remove and re-insert the psmouse. The PS/2 touchpad input device won't be registered.

Status changed to 'Confirmed' because the bug affects multiple users.

YC, can you post the output from xinput?

The attached file is the xinput output of XPS13.

Status changed to 'Confirmed' because the bug affects multiple users.