Write design/steam-deck-passthrough-plan.md — the build plan to ship exact Steam
Deck pass-through from the Linux client (incl. the Steam + QAM buttons) plus a
virtual Deck on any Linux host. Key validated facts captured so the next session
doesn't re-investigate:
- Client capture is ALREADY correct: SDL3 maps Steam->Guide, QAM->Misc1; the
client forwards BTN_GUIDE/BTN_MISC1; the host maps them to btn::STEAM/btn::QAM.
Only precondition: Steam Input disabled on the client (the Decky UX).
- Shippable host transport = usbip + vhci_hcd (in-tree + signed everywhere, no
module build, no MOK) — PROVEN on Bazzite: Steam promotes the usbip interface-2
Deck (XInput slot + X-Box pad), identical to raw_gadget on SteamOS.
- Build steps: refactor steam_gadget.rs into shared Deck-logic + a transport
trait; add the usbip transport (vendor-trim the usbip crate to drop rusb/libusb,
in-process vhci attach); transport-select raw_gadget->usbip->UHID/DualSense;
client leave-shortcut (controller chord + Ctrl+Alt+Shift+D); serial polish.
Also checks in the working usbip Deck PoC (packaging/linux/steam-deck-gadget/
usbip-poc/) for the next session to build on. Not pushed.
Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>
The virtual Steam Deck is validated glass-to-glass on a Deck: it appears as a
distinct second Steam controller, a held A drives Steam's overlay ("Resume
Game"), and a button press registers in a real game (confirmed in-game).
gadget_preferred() now defaults ON for SteamOS hosts (/etc/os-release ID=steamos
or ID_LIKE), OFF elsewhere where the universal UHID path stays the default;
PUNKTFUNK_STEAM_GADGET=1/0 forces it. A Deck-as-host with a physical Deck never
reaches this path — resolve_gamepad's conflict gate degrades SteamDeck → DualSense
first, so the two-Deck case never happens in production (it was only a test-rig
confound on the dev Deck).
The feature is complete: a virtual Steam Deck that Steam Input recognizes +
promotes, churn-free, with input flowing to games. Workspace clippy/fmt/test
green. Not pushed.
Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>
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>
The interface-2 wall is climbed. packaging/linux/steam-deck-gadget/deck_raw_gadget.c
is a raw_gadget userspace emulator of a real 3-interface USB Steam Deck (28DE:1205,
mouse=0/keyboard=1/controller=2) on a dummy_hcd loopback UDC, with descriptors
captured verbatim from a physical Deck and full HID feature-report handling.
Live on a real Deck (SteamOS 3.8.11): hid-steam reads our serial (PFDECK000),
creates the Steam Deck + Motion Sensors evdevs, and Steam Input PROMOTES it —
controller.txt "Interface: 2 ... device opened ... reserving XInput slot 1" +
"input: Microsoft X-Box 360 pad 1". Stable (1 connect, 0 disconnects, no zombie);
the kernel Steam Deck evdev is then grabbed by Steam Input which exposes its own
X-Box pad, exactly like a real Deck. First time a virtual Deck is fully Steam-Input
promoted (UHID can't — it has no USB interface number, so Steam filters it).
Also includes the configfs f_hid variant (configfs_gadget_up/down.sh) — the minimal
reproducer that proved interface 2 makes Steam open+XInput-reserve the device, but
f_hid can't serve feature reports so Steam dropped it as a zombie.
Gotchas documented in the README: 7-byte vs 9-byte endpoint descriptor, no-data OUT
controls acked via zero-length EP0_READ (not WRITE, else error -110), streamer must
not start before SET_CONFIGURATION is acked. SteamOS-host only (needs dummy_hcd +
raw_gadget). Recognition proven; feeding real client reports + a host backend is next.
Not pushed.
Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>
enricobuehler