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>
