[PATCH v4 0/2] Input: add support for OnePlus/OPPO Pad pogo-pin keyboards

[wyibo6109@gmail.com]

From: Yibo Wang <wyibo6109@gmail.com>

This series adds support for the magnetic pogo-pin smart keyboards of
the OnePlus Pad 3 Pro / Pad 4 and the OPPO Pad 5 Pro.  The keyboard is
built around a Tinno MCU attached to a tablet UART.  Both sides share a
single data wire, so the host gates its transmission onto the bus with a
PMIC GPIO for the duration of a frame, and every host frame is echoed
back on RX.

The MCU speaks a framed "one wire bus" protocol over the half-duplex
921600 8N1 UART: 8x 0x55 preamble, 0xF1, src/dst addresses, command,
length, payload, CRC16-IBM (poly 0x8005, init 0xC596), 0xFE and 4x 0xAA.
The protocol was reverse engineered from the vendor kernel driver; this
is a clean-room serdev reimplementation that replaces the downstream
platform driver, which depends on a private msm_geni_serial callback and
a user-space held tty fd.

The core protocol (framing, keys, touchpad, sync/heartbeat) has been
carried unchanged across four SoC generations of these keyboards, from
the sm8550 era to the sm8850 ones covered here; only the 0x3A general
sub-commands grew over time.  Patch 1 adds the DT binding, patch 2 the
driver.

Changes in v4, after Krzysztof Kozlowski's comment that the binding
describes the keyboard rather than the MCU (wording only, no functional
change):

- the binding description and the commit messages now describe the
  keyboard (built around the Tinno MCU) instead of the MCU itself, and
  spell out that a keyboard is a fixed physical device, so the touchpad
  geometry and the product names are per-compatible constants in the
  driver.

Changes in v3:

- the compatible names the tablet project the pogo port belongs to
  (oneplus,caihong- / erhai- / iceland-pogo-keyboard, the codenames
  used by the vendor trees), and the driver carries a per-project
  description in the OF match data: feature flags gate each 0x3A
  general sub-command (caihong, sm8650 era, has no wake notification
  and no backlight; erhai, sm8750 era, adds the wake notification;
  iceland, sm8850 era, adds the keyboard backlight), while the touchpad
  geometry and the per-brand product names are per-project constants -
  the wake notification is skipped and the backlight LED only
  registered where supported;

- the touchpad geometry and product names are no longer DT properties:
  they are fixed per project and live in the driver; the common
  touchscreen properties (touchscreen-size-x/y, touchscreen-x-mm/y-mm)
  remain as an optional override, parsed with
  touchscreen_parse_properties(), for the unlikely case of a variant.

Changes in v2:

- dropped the redundant "binding" from the dt-bindings subject;

- replaced the custom oneplus,touchpad-xy-max/-resolution properties
  with the common touchscreen properties;

- dropped the serial wrapper node from the binding example;

- the MAINTAINERS entry added with the binding references only the
  binding file; the driver F: line is added together with the driver
  patch.

Tested on the OnePlus Pad 4 (iceland) running Linux 7.2.0-sm8850
(v7.2-based iceland tree).

Yibo Wang (2):
  dt-bindings: input: add OnePlus pogo-pin keyboard
  Input: add OnePlus/OPPO Pad pogo-pin keyboard serdev driver

 MAINTAINERS                                   |    7 +
 .../bindings/input/oneplus,pogo-keyboard.yaml |   73 +
 drivers/input/keyboard/Kconfig                |   13 +
 drivers/input/keyboard/Makefile               |    1 +
 drivers/input/keyboard/oneplus-pogo-kbd.c     | 1263 +++++++++++++++++
 5 files changed, 1357 insertions(+)
 create mode 100644 Documentation/devicetree/bindings/input/oneplus,pogo-keyboard.yaml
 create mode 100644 drivers/input/keyboard/oneplus-pogo-kbd.c

-- 
2.53.0