SM8550: AYN Odin 2 - expose the two back buttons as gpio-keys

[xiaodoudou]

Summary

• Goal: Make the AYN Odin 2's two back buttons (M1, M2) work. On stock ROCKNIX they emit nothing because there is no driver for them. This replicates SM8750: AYN Odin 3 - expose the two back paddles as gpio-keys #2940 (AYN Odin 3) on SM8550: a gpio-keys-paddles node in the Odin 2 dts so they report buttons.
• They are not on the gamepad MCU UART (rsinput) and not ADC despite AYN's Android adckey/keydetect.ko naming — they are plain active-low SoC TLMM GPIOs: M1 = GPIO 57 → BTN_Z, M2 = GPIO 58 → BTN_C (TLMM base 301 + offsets 57/58, RE'd from AYN's keydetect.ko gpio_request(358/359) and confirmed on hardware by watching the TLMM GPIO_IN registers while pressing the buttons).
• Mirrors the Odin 3 InputPlumber integration on the SM8550 side: source the new device in 02-ayn-controller.yaml, route BTN_Z/BTN_C to Left/RightPaddle2 in ayn_mcu.yaml, and switch the target to ds5-edge so the buttons are emitted as the DualSense Edge's real back-lever buttons (hid-playstation Edge support from patches/mainline/0006 already applies to SM8550 kernels).

Testing

• Pin discovery and end-to-end flow verified on an AYN Odin 2 base running ROCKNIX next 20260701: an equivalent runtime GPIO driver for pins 57/58 produces clean press/release (evtest) with no chatter, and the events reach the virtual controller through InputPlumber's AYN composite.
• This dts: compile-tested against linux-7.1.2 + the full SM8550 patch set (qcs8550-ayn-odin2.dtb builds; decompiled blob contains the node). I could not build a full image — happy to flash a CI artifact on my Odin 2 and report back.

Additional Context

• Same scheme as SM8750: AYN Odin 3 - expose the two back paddles as gpio-keys #2940 — thanks @aanze for the template. Odin 2 differs only in SoC, pins (57/58) and vendor gpiochip base (301).
• Pins referenced by TLMM offset (<&tlmm 57>, <&tlmm 58>), input + pull-up, 15ms debounce.
• The ds5-edge target / Paddle2 changes are in the shared SM8550 AYN files also covering Odin 2 Mini / Odin 2 Portal / Retroid Pocket 6 — cosmetic for devices without the buttons (presents as an Edge with unused levers), same situation as SM8750. Happy to split per-device if preferred.
• Only the base Odin 2 dts gains the node; Mini/Portal very likely share the wiring but I don't own them to test.

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AI Usage

Did you use AI tools to help write this code? PARTIALLY — reverse-engineering and patch authoring assisted by AI; hardware findings verified on-device.