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I have a new DELL Latitude 7490 with Ubuntu 18.04.1 and I am experiencing a little annoying bug related to the touchpad. When I don't use it for some time (more than 3~4 seconds), if then I sweep quickly my finger on it, the cursor gest "teleported" to his final position, without actually showing the path. It feels like the touchpad goes to a sort of "sleep mode", and then when it wakes up there is a small, but perceptible, lag that makes this jump of the cursor to happen. If I use the touchpad continuosly this does not happen, but only after some seconds of inactivity. The same behavior happens with the trackpad (the "nipple").

I don't really know what to do, I tried updating the Linux kernel and changing all the possible libinput options, with no success. Have you got any suggestions?

Tropilio
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1 Answers1

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I have the same Notebook, but running it with the arch based distro Manjaro. I used to have the same annoying behaviour and with the help of the great forum support of manjaro, we found a solution, which will probably help you too.

The culprit is the power management tlp. There, after a few seconds, some input devices were send to sleep after a few seconds.

I think tlp is the same like in manjaro as it is in ubuntu and so the solution will be the same or easily customizable for Ubuntu.

(thanks to the manjaro volunteer dgit):

sudo nano /etc/default/tlp

This lets you edit the tlp settings. You should find the line below and edit it like that:

RUNTIME_PM_DRIVER_BLACKLIST="amdgpu nouveau nvidia radeon pcieport i2c_hid hid_multitouch serio i8042 psmouse atkbd synaptics hid_multitouch"

You see, these is a driver blacklist, which excludes now our input devices (touchpas and trackball).

You can now save this with CTRL+X, hit Y to succeed and write in the terminal:

sudo systemctl enable tlp

Then reboot and the touchpad should always be working on first touch.

So, but now we also want to make it work, when we dont use it in AC mode, but on battery. Again, switch to edit the tlp setting, look for the following line and edit it like that:

# Runtime Power Management for PCI(e) bus devices: on=disable, auto=enable.
RUNTIME_PM_ON_AC=on 
RUNTIME_PM_ON_BAT=on

Here is the original link to the forum:

Dell 7490 Touchpad Issue lag at use after 3-4 seconds

Again, give credits to user dgit or if you ever on the streets, give him a hug.

Charles Green
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hundsboog
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