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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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  • Try running libinput debug-events --verbose, and then reproduce the problem. It should record any motion you do; do you see prints between the moment you touched the touchpad, and the moment cursor got "teleported"? If you don't, try repeating it with evemu-record command — are prints present there? – Hi-Angel Jan 26 '19 at 21:18
  • @Hi-Angel Hi, thanks for your help. No, I don't see any prints during the lag in neither of the two commands. When the cursor gets "teleported" a bunch of prints appear all at once. – Tropilio Jan 26 '19 at 21:47
  • Then it's likely a hardware problem. Still, it's possible that it can be worked around with ACPI and what not quirks, so I'd recommend to test with latest stable mainline kernel (4.20.5 at the moment), and then report a bug to bugzilla.kernel.org, "Product: drivers", "Component: Input Devices". – Hi-Angel Jan 26 '19 at 23:01
  • @Hi-Angel What do you mean by hardware problem? Under Windows it was not showing this delay. – Tropilio Jan 27 '19 at 01:26
  • Okay, then the touchpad probably requires some quirk to work correctly. I doubt an arbitrary person here can help with this (I can't), the best way to move forward would be the bug report. If you do report it, please add the link here, so that peoples with a similar problem could navigate straight to the report. – Hi-Angel Jan 27 '19 at 10:55
  • FWIW, it's interesting that other users don't seem to have the problem. It's another point to try installing latest mainline kernel, and see whether it works there. – Hi-Angel Jan 27 '19 at 10:58
  • @Hi-Angel I just tried installing the latest kernel and the problem is still there... I'll try opening a bug report. Thanks for your help! – Tropilio Jan 27 '19 at 11:51

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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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  • A couple of notes about this: 1) It assumes Tlp is installed, and Tlp is not installed be default in Ubuntu. 2) systemctl enable tlp is redundant if Tlp has been installed and running prior to your changes. sudo tlp start aould be sufficient, and a reboot is not required. – Charles Green Mar 12 '19 at 13:24