Thinkpad t480s elantech touchpad device is not recognized: unknown touchpad firmware (firmware v.0x7f3001)

[Andrey Kosachenko]

Hi,

Recently I've replaced my t410 with t480s model.
Before ordering the device I found positive feedback in terms of FreeBSD 
compatibility (pages like https://wiki.freebsd.org/Laptops/Thinkpad_T480)

Apparently device is equipped with newer clickpad+trackpoint device 
which is not recognized by 12R properly:

FreeBSD beastie.intra 12.0-RELEASE-p3 FreeBSD 12.0-RELEASE-p3 #2 
r347114M: Sun May 12 00:08:31 EEST 2019 
root at beastie.intra:/usr/obj/usr/src/amd64.amd64/sys/BEASTIE-EVDEV  amd64

Attempts to enable hw.psm.synaptics_support or(and) 
hw.psm.elantech_support didn't help either. Though  trackpoint works 
just fine after enabling hw.psm.trackpoint_support

instead touchpad is recognized as generic PS/2 mouse (relevant strings 
from dmesg)

===
May 11 22:39:41 beastie kernel: atkbd0: [GIANT-LOCKED]
May 11 22:39:41 beastie kernel:   Unknown touchpad hardware (firmware 
v.0x7f3001)
May 11 22:39:41 beastie kernel: psm0: <PS/2 Mouse> irq 12 on atkbdc0
May 11 22:39:41 beastie kernel: psm0: [GIANT-LOCKED]
May 11 22:39:41 beastie kernel: psm0: model Generic PS/2 mouse, device ID 0
===

I was pretty much happy working with the device in general and with the 
tuouchpad in particular (as a simple mouse). Even got accustomed to the 
absence of double-finger scroll capability (which I could simulate via 
holding mid-button+swipe on touchpad) and triple-finger-tap as a 
midle-button-click). The only thing that I failed to workaround was 
accidental palm touches which is really painful and makes keyboard usage 
unbearable. Eventually I tried to seek for normal solution.

Lenovo site sujests for t480s devices "ELAN UltraNav Driver for Windows 
10 64-bit - ThinkPad T480s (Type 20L7, 20L8)" driver. Which made me 
think it is elantech (not synaptics). Looking through the psm sources 
quickly led me to the point where a very simple modification and 
recompilation of the kernel helped to recognize touchpad properly. In 
particular:

===
[silent at beastie][/usr/src]svnlite diff sys/dev/atkbdc/psm.c
Index: sys/dev/atkbdc/psm.c
===================================================================
--- sys/dev/atkbdc/psm.c        (revision 347114)
+++ sys/dev/atkbdc/psm.c        (working copy)
@@ -6929,7 +6929,7 @@
  {
         static const int ic2hw[] =
         /*IC: 0  1  2  3  4  5  6  7  8  9  a  b  c  d  e  f */
-           { 0, 0, 2, 0, 2, 3, 4, 4, 4, 4, 4, 4, 4, 4, 4, 0 };
+           { 0, 0, 2, 0, 2, 3, 4, 4, 4, 4, 4, 4, 4, 4, 4, 4 };
         static const int fw_sizes[][3] = {
                 /* FW.vers  MaxX  MaxY */
                 { 0x020030, 1152,  768 },
===

I.e. after that simple modification system started to recognize fw version:

===
[silent at beastie][/usr/src]dmesg | egrep psm
psm0: <PS/2 Mouse> irq 12 on atkbdc0
psm0: [GIANT-LOCKED]
psm0: model Elantech Touchpad, device ID 0
===

and all expected touchpad features (multi-tap gestures and scrolling, 
whatsoever) started to function properly under xorg+evdev. I'm happy 
with a touchpad now however trackpoint stopped to work. In particular 
attempt to use trackpoint causes strange flickering of the mice cursor 
(which lasts few fractions of the second) after which cursor jumps to 
the left-upper corner of the screen and it's impossible to move it (via 
trackpoint) anymore (though swiping touchpad surface moves cursor as 
expected). Also I found in Xorg.log messages emerging when a palm 
touches the surface of a touchpad:

===
[    65.729] (EE) event3  - ETPS/2 Elantech Touchpad: kernel bug: Touch 
jump detected and discarded.
See 
https://wayland.freedesktop.org/libinput/doc/1.12.6/touchpad-jumping-cursors.html 
for details

===


Additionally I found relevant topic in openbsd lists 
http://openbsd-archive.7691.n7.nabble.com/ThinkPad-T480s-Elantech-v4-clickpad-configuration-td342242.html. 
Eventually I narrow down it to the following changes: 
https://github.com/openbsd/src/commit/8e9e9c10431cb45d93e2c0d81f668ff9575f8015#diff-ff06b79b08490ebbfa34b15aa4ebf370 
. I might be inherently wrong (due to lack of knowledge in C language 
and driver implementation) however it seemed to me that the similar 
logic the diff above reveals (besides fw detection) had already been 
added to psm.c from FreeBSD sources earlier.


So I'm writing here for 2 purposes:

1) not sure that my modification is proper in terms of firmware version 
detection (so can't send patch since there is a high chance it will be 
rejected)

2) modification is definitely either incomplete or incorrect since it 
brakes trackpoint functioning.

Since I possess a laptop with a device which is not supported yet, I 
might help to debug the issue or even dedicate some time and try to add 
support for a new device (just need a nudge into proper direction)

Thanks in advance!

--
WBR,
Andrey Kosachenko