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>
enricobuehler
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