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feat(host/steam): default the gadget Deck on for SteamOS (glass-confirmed)

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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>
This commit is contained in:
Enrico Bühler
2026-06-29 16:32:42 +00:00
parent 7ab8acaf55
commit 963c406f33
4 changed files with 39 additions and 11 deletions
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packaging/linux/steam-deck-gadget/README.md
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@@ -56,14 +56,17 @@ Steam Input, which exposes its own X-Box 360 pad — exactly a real Deck's behav
`EP_WRITE` starves the control path.
- `dummy_hcd` + `raw_gadget` must both be loaded and `/dev/raw-gadget` present before launch.
## Host backend (shipped, opt-in)
## Host backend (shipped — default on for SteamOS)
The C PoC's transport is ported to a Rust host gamepad backend:
`crates/punktfunk-host/src/inject/linux/steam_gadget.rs` (`SteamDeckGadget`), driven by the same
`steam_proto` serializer as the UHID `SteamDeckPad`. The Steam-Deck manager
(`inject/linux/steam_controller.rs`) now selects per-pad between **UHID** (default, universal) and the
**USB gadget** (`PUNKTFUNK_STEAM_GADGET=1`, SteamOS-only — best-effort `modprobe dummy_hcd raw_gadget`,
graceful fallback to UHID if `/dev/raw-gadget` is unusable).
(`inject/linux/steam_controller.rs`) selects per-pad between **UHID** (universal) and the **USB
gadget**: the gadget is the **default on SteamOS hosts** (`gadget_preferred()` → `ID=steamos`;
best-effort `modprobe dummy_hcd raw_gadget`, graceful fallback to UHID if `/dev/raw-gadget` is
unusable), and off elsewhere where UHID stays the default. `PUNKTFUNK_STEAM_GADGET=1`/`0` forces it.
A Deck-as-host with a *physical* Deck never uses it — `resolve_gamepad`'s conflict gate degrades
`SteamDeck` → DualSense first.
The Rust transport is **validated on the Deck** (a static musl test binary that `#[path]`-includes the
real module): it enumerates the 3-interface Deck, hid-steam binds it + reads our serial + creates the