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https://github.com/kuhyx/testsAndMisc.git
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Krzysztof kuhy Rudnicki
c81e4a9446
BeamNG.drive 0.39 native lost G29 FFB because SDL3's HIDAPI lg4ff driver advertises an effect-status query it cannot answer (12,201 failures per session in beamng.log). DOCS-g29-ffb.md records the diagnosis, the narrow SDL_JOYSTICK_HIDAPI_LG4FF=0 hint vs the broad one, and the launch-option %command% bug that had gamemoderun passed as a game argument. install_new_lg4ff.sh swaps the in-tree hid-logitech for new-lg4ff via DKMS (dkms.conf installs it under the same name in updates/dkms/), regenerates initramfs presets that bundle the module, and offers --status/--revert. Passed install/status/revert in vmbox; host run pending. Co-Authored-By: Claude Opus 5 (1M context) <noreply@anthropic.com> Claude-Session: https://claude.ai/code/session_01SS8M5wk88nJTXxDWz61KKk
106 lines
5.1 KiB
Markdown
106 lines
5.1 KiB
Markdown
# Logitech G29: no force feedback in BeamNG.drive (native Linux)
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Files: `fixes/install_new_lg4ff.sh` (optional driver upgrade),
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`~/src/steam-backlog-enforcer/steam_backlog_enforcer/_desktop_env.py` (the
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host-level env var). Shifter companion: `DOCS-g29-shifter.md`.
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## Symptom
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BeamNG.drive 0.39.x, **native Linux build** (not Proton): the G29 steers,
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pedals and buttons work, but the wheel is limp — no resistance, no
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self-centring. Other games with FFB are unaffected.
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## Cause (measured 2026-09-14, BeamNG 0.39.4.0, SDL 3.4.12 static)
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`~/.local/share/BeamNG/BeamNG.drive/current/beamng.log`:
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```
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D|logHapticFeatures| Device joystick3 supports the following ffb features:
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Constant Sine Triangle SawToothUp SawToothDown Spring Damper Friction Status Query
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I|inputRegistry| Created ffbid 0, ... on device joystick3 with axis id=0
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E|updateFrame| Failed to get joystick3 FFB effect status: (x12,201 per session)
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```
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That feature list is SDL3's **HIDAPI lg4ff** driver (`SDL_hidapi_lg4ff.c`),
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which talks to the wheel over hidraw and bypasses the kernel `hid-logitech`
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driver — the kernel driver advertises only constant/gain/autocenter
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(`capabilities/ff` = `300040000 0`). The hidapi haptic backend advertises a
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status query it cannot answer; BeamNG polls it every frame, gets an error, and
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treats the effect as dead. Known regression:
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<https://www.beamng.com/threads/ffb-not-working-on-linux.110807/>.
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Not involved: the shifter HID-BPF (input direction only), hidraw permissions
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(SDL had already opened the device), Proton (not used).
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## Fix: make SDL use the kernel driver
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Two env vars exist; they are not interchangeable:
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| var | scope | use |
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| ----------------------------- | ------------------------------------- | -------------------------------------------------------------------------- |
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| `SDL_JOYSTICK_HIDAPI_LG4FF=0` | only the Logitech-wheel HIDAPI driver | **host-level**: set for every game, gamepads keep HIDAPI (BT rumble, LEDs) |
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| `SDL_JOYSTICK_HIDAPI=0` | all of SDL's HIDAPI joystick drivers | forum-proven fallback, per-game only |
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Both names verified against strings in `BinLinux/BeamNG.drive.x64`.
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1. **Per game** — Steam → BeamNG.drive → Properties → Launch Options:
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```
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SDL_JOYSTICK_HIDAPI_LG4FF=0 LSFG_PROCESS=BeamNG.Drive gamemoderun %command%
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```
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The previous value had no `%command%`, so Steam appended
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`LSFG_PROCESS=... gamemoderun ./BinLinux/BeamNG.drive.x64` as _arguments_
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to the game (visible in `pgrep -a BeamNG.drive.x64`) and neither gamemode
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nor LSFG was ever applied.
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2. **Host level** — Steam on this machine is started by
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`steam-backlog-enforcer` through `sudo -u kuhy env <allowlist> steam …`.
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`sudo`'s `env_reset` makes that list the entire environment Steam and every
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game sees, so `/etc/environment`, `~/.profile` or `~/.pam_environment`
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never reach it. The variable lives in `desktop_env_args()` in the
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enforcer's `_desktop_env.py`. Check it landed:
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```bash
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tr '\0' '\n' < /proc/$(pgrep -x steam)/environ | grep LG4FF
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```
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A missing line means Steam predates the enforcer change — it takes effect
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on the next Steam launch (`systemctl restart steam-backlog-enforcer` kills
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a running game; check `pgrep -f BeamNG.drive.x64` first).
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## Verify
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- Game-independent motor check, BeamNG closed:
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`fftest /dev/input/by-id/usb-Logitech_G29_Driving_Force_Racing_Wheel-event-joystick`
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— effects 0 (constant) and 4 (autocenter) must move the wheel.
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- In a fresh `beamng.log` the haptic feature line becomes the kernel-style
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list and `grep -c 'FFB effect status' beamng.log` drops to 0. A non-zero
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count with working force is fine; a zero count with no force is not.
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- The gate is physical: drive a car, feel resistance and centring.
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## Optional: new-lg4ff instead of the in-tree driver
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`fixes/install_new_lg4ff.sh` installs `new-lg4ff-dkms-git` (AUR). Its
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`dkms.conf` sets `DEST_MODULE_NAME="hid-logitech"`, so DKMS places it in
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`updates/dkms/` and it shadows the in-tree module _by name_ — no blacklist,
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no `modules-load.d`. Once loaded it registers as `hid_logitech_new`. Adds
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spring/damper/friction/periodic effects and the `spring_level` /
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`damper_level` / `friction_level` / `gain` / `autocenter` sysfs knobs.
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Traps the script handles:
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- `mkinitcpio`'s `autodetect` hook bundles `hid-logitech` into the initramfs
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because the wheel is plugged in at build time; a stale in-tree copy there
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would load first at boot. The script regenerates the presets when an image
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carries the module.
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- `dkms status <name>` is a prefix filter that prints _everything_ on a miss;
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always grep `dkms status` output.
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- USB interface 1 of the G29 (`0003:046D:C24F.0007`) is unbound by design.
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```bash
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~/src/testsAndMisc/linux_configuration/fixes/install_new_lg4ff.sh # install (runs yay; needs a TTY)
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~/src/testsAndMisc/linux_configuration/fixes/install_new_lg4ff.sh --status # which module owns the wheel + ff caps
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~/src/testsAndMisc/linux_configuration/fixes/install_new_lg4ff.sh --revert # pacman -Rns + reload, no reboot
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```
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