The virtual Deck's gamepad evdev was churning (destroyed + recreated) because
Steam kept re-probing: GetControllerInfo reads HID feature reports, and the gadget
served zeros for them. Captured the real contract off a physical Deck
(packaging/linux/steam-deck-gadget/get_deck_attrs.c, hidraw HIDIOCGFEATURE — usbmon
truncates to 32B) and implemented it in steam_gadget.rs::feature_reply:
- 0x83 GET_ATTRIBUTES_VALUES: [83, 2d, 9×(attr-id, u32-LE)] — product id 0x1205, a
per-instance unit serial (0x0a/0x04, so a gadget never collides with a real Deck
or another gadget), and the capability attrs (0x09=0x2e, 0x0b=0x0fa0, rest 0).
- 0xAE GET_STRING_ATTRIBUTE: [ae, len, attr, ascii] — serial (attr 1) / board
serial (attr 0).
- other commands (0x87 settings): echo the last write.
Validated on the Deck: 1 connect / 0 disconnect / 1 gamepad evdev (was constant
churn), Steam activates the gadget cleanly (no GetControllerInfo failed, no zombie)
and emits its X-Box 360 pad. usbmon on the gadget's bus confirms our state reports
(pressed button at byte 8) are delivered on the interrupt-IN and consumed by
hid-steam — so with M1/M2's byte-8→BTN_SOUTH decode the input chain is proven
end-to-end. Remaining: a foreground-game confirmation of Steam Input's XInput
mapping, then default the gadget on for SteamOS.
Workspace clippy/fmt/test green. Not pushed.
Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>
Port the proven raw_gadget virtual Deck to a Rust host gamepad backend, the
SteamOS-only transport that gets Steam Input to actually promote the Deck.
- inject/linux/steam_gadget.rs (new): SteamDeckGadget — a userspace raw_gadget
emulator of the real 3-interface USB Deck (mouse=0/keyboard=1/controller=2,
28DE:1205) on a dummy_hcd loopback UDC, descriptors captured from a physical
Deck, answering every control transfer incl. the HID feature reports. Driven by
the same steam_proto::serialize_deck_state as the UHID pad; rumble feedback via
parse_steam_output. The raw_gadget UAPI is funneled through 4 documented ioctl
wrappers (the crate denies undocumented unsafe).
- inject/linux/steam_controller.rs: the manager pad is now a DeckTransport enum
(Uhid | Gadget); ensure() prefers the gadget when PUNKTFUNK_STEAM_GADGET=1
(best-effort modprobe dummy_hcd+raw_gadget), gracefully falling back to the
universal UHID SteamDeckPad. write/pump/heartbeat dispatch through the enum.
Validated on a real Deck via a static musl harness that #[path]-includes the
module: enumerates, hid-steam binds + reads our serial + creates the Steam Deck +
Motion Sensors evdevs — identical to the C PoC. Caught a real portability bug:
raw_gadget's no-arg ioctls (RUN/CONFIGURE/EP0_STALL) reject a non-zero `value`
with EINVAL, and on musl an omitted ioctl vararg is a garbage register — so they
must pass an explicit 0.
Opt-in (default off) while the Steam GetControllerInfo feature contract is
hardened (to stop the gamepad-evdev churn). Workspace clippy/fmt/test green. Not pushed.
Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>
enricobuehler