[Bug] Legion Go 2: controller disconnect loop — touchpad matched by BTN_MOUSE but hid-lenovo-go exposes BTN_TOUCH

[MasterGenotype]

Related: #226 (Legion Go 2 Support tracker)

Summary

On a Lenovo Legion Go 2 (17ef:61eb) using the in-kernel hid-lenovo-go driver, HHD's
Legion Go handler crash-loops every ~3 s with "Assuming controllers disconnected, restarting
after 3s". The controller repeatedly disconnects/reconnects and is unusable in game mode.

Root cause: HHD's d_touch device definition requires the touchpad evdev node to report
BTN_MOUSE (272), but on the Go 2 the hid-lenovo-go driver exposes the touchpad as a real
touchpad reporting BTN_TOUCH (330) instead. The match fails, and because required=True
this raises RuntimeError and restarts the controller forever.

Environment

• Device: Lenovo Legion Go 2 — 17ef:61eb
• HHD: 4.1.8+17.r2628.20260319.52968948 (git)
• Kernel (build & version):
  • uname -r: 7.2.0-273-tkg-bore
  • uname -v: #1 SMP PREEMPT_DYNAMIC TKG Thu, 27 Aug 2026 01:57:28 +0000
  • Custom linux-tkg (Frogging-Family) build with the BORE scheduler; package
    linux72-tkg-bore 7.2.0-273; built with gcc 16.1.1 / binutils 2.46.1.
• HID driver (important): the touchpad is claimed by hid-lenovo-go ("HID Driver for
  Lenovo Legion Go Series Gamepads", author Derek J. Clark), bundled in this TKG kernel
  (/lib/modules/7.2.0-273-tkg-bore/kernel/drivers/hid/hid-lenovo-go.ko.zst, owned by
  linux72-tkg-bore 7.2.0-273, srcversion E45DE305EDB0FB5D61A7C55). This driver's device
  presentation — touchpad as BTN_TOUCH rather than BTN_MOUSE — is central to the bug, so the
  exact kernel/driver build matters for reproduction.
• Distro: Artix Linux (runit)

Symptom (HHD log)

LLGO ERROR  Device with the following not found:
              Vendor ID: ['17ef']
              Product ID: ['6182', '61eb']
              Name: [re.compile('.+Touchpad')]
              Capabilities: {1: [272]}          # EV_KEY: BTN_MOUSE
LLGO ERROR  <class 'RuntimeError'>:
LLGO ERROR  Assuming controllers disconnected, restarting after 3s.

This repeats indefinitely; downstream, Steam Input keeps re-creating its virtual
"Microsoft X-Box 360 pad" on every cycle.

Root cause

hhd/device/legion_go/tablet/base.py, in controller_loop_xinput:

d_touch = GenericGamepadEvdev(
    vid=[0x17EF],
    pid=[0x6182, 0x61EB],
    name=[re.compile(".+Touchpad")],
    capabilities={EC("EV_KEY"): [EC("BTN_MOUSE")]},   # requires BTN_MOUSE (272)
    ...
    required=True,
)

But the actual Go 2 touchpad node does not report BTN_MOUSE — it reports BTN_TOUCH:

N: Name="  Legion Controller for Windows  Touchpad"
H: Handlers=event4 mouse1
B: KEY=400 1 0 0 0 0     # top word bit 0x400 -> code 330 = BTN_TOUCH; no bit for 272 (BTN_MOUSE)
B: ABS=10000000003       # ABS_X, ABS_Y + MT axis

For comparison, on this device it is the separate Mouse node that carries BTN_MOUSE:

N: Name="  Legion Controller for Windows  Mouse"
B: KEY=1f0000            # BTN_LEFT/RIGHT/MIDDLE/SIDE/EXTRA (272–276)

So no single node satisfies both name ~ .+Touchpad and has BTN_MOUSE, and with
required=True the mismatch becomes a fatal restart loop.

This looks like the touchpad definition predates the hid-lenovo-go driver's device
presentation on the Go 2 (original Legion Go exposed the touchpad as a mouse; the Go 2 driver
exposes it as a proper BTN_TOUCH touchpad).

Suggested fix

Match the Go 2 touchpad correctly, e.g. accept BTN_TOUCH for this device (and/or verify the
touchpad axis map for the Go 2). If a separate Go 2 code path is preferred, gate on the
hid-lenovo-go presentation. As a safety measure, consider not making the touchpad
required=True so a touchpad-detection miss degrades gracefully instead of crash-looping the
whole controller.

Workaround (confirmed)

Setting the d_touch entry to required=False stops the loop; the controller (sticks,
buttons, gyro, emulated DualSense) works, only the DualSense touchpad passthrough is lost.

Extra diagnostics available

Happy to provide full hhd logs, the complete /proc/bus/input/devices dump, evtest output
for the touchpad node, or hid-lenovo-go details on request.