Gate accelerometer auto-rotation on tablet mode (X11 + Wayland)

[ggiesen]

What

Cinnamon already auto-rotates the built-in panel from the accelerometer (Muffin's MetaOrientationManager + MetaMonitorManager), gated only by orientation-lock. On a convertible that means it rotates in every posture — it never checks the tablet-mode switch, so the screen flips while the device is used as a laptop.

This gates auto-rotation on tablet mode:

• apply_orientation() now consults ClutterSeat:touch-mode (true only when a touchscreen is present and the device is in tablet mode or has no tablet-mode switch) plus a new disable-rotation-in-laptop-mode key, and honours orientation-lock on the touch-mode / setting-change paths.
• The native/Wayland backend already exposes touch-mode from libinput. The X11 backend had no source for SW_TABLET_MODE, so meta-seat-x11.c now reads the evdev switch directly (by capability, with hot-plug recovery and the login-ACL race handled) and folds it into touch-mode — so the same gate works under X11, where Cinnamon mostly runs today.

Devices with no tablet-mode switch (slates) are unaffected — touch-mode is true, so they keep auto-rotating.

Context / prior art

This is the feature from #10697 (cinnamon) / cinnamon-settings-daemon#359. The earlier PRs — cinnamon#10708 and cinnamon-settings-daemon#361 — implemented it in the csd orientation plugin, which was being removed as the orientation work moved into Muffin (the reason they were closed). This does it in Muffin, where rotation now lives.

Two small companion changes are needed (happy to open as linked PRs):

• cinnamon-settings-daemon: add disable-rotation-in-laptop-mode (bool, default true) to the …peripherals.touchscreen schema (5 lines).
• cinnamon: surface it in Display → Settings. In #10697 @mtwebster suggested a 3-way combobox (Disabled / Enabled / Tablet mode only) instead of a second toggle — glad to do exactly that.
• X11 needs a uaccess udev rule so Muffin can read the switch as the session user (rule included in the companion repo below).

Validation

Built as patched packages and dogfooded on an HP ZBook Studio x360 G5 (Mint 22.3, Cinnamon 6.6.7, Muffin 6.6.3, X11): rotation and tablet-mode gating handled entirely by Muffin, no external daemon. Rebased onto and applies cleanly to master (6.7.3). Full patch set, udev rule, and build notes: https://gitlab.com/ggiesen/cinnamon-autorotate

Feedback welcome

This is a proposal as much as a patch — happy to take feedback or change direction on any of it: the combobox-vs-toggle UX, the key name/layout, splitting the X11 seat change into its own commit, or sending the Wayland-gating part upstream to GNOME Mutter as well. Just point me at what fits Cinnamon best.

[ggiesen]

Companion PRs now open: schema key in cinnamon-settings-daemon#463, and the Display Automatic screen rotation combobox in cinnamon#13826 (the UI @mtwebster suggested in linuxmint/cinnamon#10697). The three go together.

[ggiesen]

Field-testing note (no code changes - recording behaviour on a second platform).

I've tested this on two HP convertibles, both Linux Mint / X11:

• ZBook Studio x360 G5 - has a reliable SW_TABLET_MODE fold switch; Tablet mode only works as intended (holds landscape as a laptop, follows the accelerometer when folded into tablet).
• Pavilion x360 14-dh1008ca - no reliable fold switch. This machine's firmware uses the screen-rotation accelerometer (the same sensor that drives auto-rotate) as its tablet-mode indicator rather than the hinge: intel-hid's SW_TABLET_MODE asserts on screen orientation (a tilt toward portrait), not on fold - the kernel dual_accel_detect() gap for ISH-hosted accelerometers - and its other (HP-WMI) switch never asserts. The firmware leans all the way into this: it locks out the internal keyboard and touchpad whenever the screen is rotated to portrait, even in laptop posture. So the machine's own notion of "tablet" genuinely is orientation, which is why erring toward rotating fits this hardware rather than fighting it.

Caveat worth documenting: "Tablet mode only" gates correctly only where the hardware exposes a real fold switch. On a machine without one it cannot distinguish laptop from tablet, so the right thing is to err toward rotating - i.e. use "Enabled", which bypasses the gate entirely (the same escape-hatch role as KWin/KScreen's tri-state Always). On no-reliable-sensor hardware Tablet mode only effectively degrades to Enabled/Always behaviour, which is the desired failure direction. I specifically do not recommend intel_hid.enable_sw_tablet_mode=0 there: it removes the only switch that ever asserts and would stop rotation altogether.

For completeness: I considered and rejected compositor-side heuristics to auto-detect bad switches - "rotate until the switch toggles" would reintroduce laptop-mode rotation at every cold boot, and persisting a "proven" flag adds state yet still wouldn't fix the orientation-coupled case (that switch does toggle). The stateless read here mirrors the native/libinput backend, so no change is warranted.