From: Zi Jie Zhao <zjzhao@edatec.cn>

Add support for the WK2xxx family of SPI to UART bridge ICs from Chengdu
Weikai Microelectronics (WKmic): WK2124, WK2132, WK2168, WK2202 and WK2204.

Base the driver on the vendor's open-source implementation:
https://github.com/britus/wk2xxx/blob/master/spi-wk2xxx.c

Use the company's website domain, http://www.wkmic.com/, for the vendor
prefix.

Describe the external reference clock with the standard "clocks" property
and model each UART as a "serial@N" child node.

Changes in v4:

- Rename the binding file to "wkmic,wk2124.yaml" so its filename matches a
  compatible string;
- Replace "clock-frequency" with a required standard "clocks" input;
- Document why individual compatible strings are retained: the two-channel
  WK2132 and WK2202 do not have the hardware flow-control and RS-485
  registers present on the four-channel variants;
- Identify the maintainer as Zi Jie Zhao and document the vendor website and
  source attribution;
- Remove the unnecessary "linux/mod_devicetable.h" include;
- Describe hardware flow control and RS-485 support per chip variant;
- Retain the v3 fixes for IRQ setup and teardown, polling lifetime, SPI error
  handling, cache-safe shared buffers, and bounded IRQ processing.

Testing:

- Run dt_binding_check with the WK2xxx binding;
- Build the driver for an ARM64 target;
- IPC12 with WK2132 on SPI0: reboot, load the driver successfully, and
  register ttyWK0 and ttyWK1 with IRQ 184 and base_baud 691200;
- SBC2300 with WK2204: run four-port TX stress and repeated module
  unload/load with closed ports.

Zi Jie Zhao (2):
  dt-bindings: serial: Document WK2xxx SPI UART
  serial: wk2xxx: Add WK2xxx SPI UART driver

 .../bindings/serial/wkmic,wk2124.yaml         |  119 ++
 .../devicetree/bindings/vendor-prefixes.yaml  |    2 +
 drivers/tty/serial/Kconfig                    |   17 +
 drivers/tty/serial/Makefile                   |    1 +
 drivers/tty/serial/wk2xxx.c                   | 1433 +++++++++++++++++
 include/uapi/linux/serial_core.h              |    3 +
 6 files changed, 1575 insertions(+)
 create mode 100644 Documentation/devicetree/bindings/serial/wkmic,wk2124.yaml
 create mode 100644 drivers/tty/serial/wk2xxx.c

-- 
2.43.0