[PATCH v5 0/2] WK2xxx SPI to UART bridge driver

[zjzhao]

From: Zi Jie Zhao <zjzhao@xxxxxxxxx>

Add support for the WK2xxx SPI to UART bridge ICs from Chengdu Weikai
Microelectronics (WKmic): WK2124, WK2132, WK2168, WK2212 and WK2204.

The public v4 series used WK2202 by mistake. The WK2202 name in the public
reference driver is a typo; the correct model is WK2212. The v5 binding and
driver use WK2212 consistently. It is a two-channel model with hardware
flow control and RS-485 support.

Huang Yang <hy@xxxxxxxxx> is listed as the primary maintainer of the driver
and binding from v5 onward. He will lead follow-up code changes and
reviewer replies, with Zi Jie Zhao providing transition support.

Changes in v5:

- Rebase onto 9b87fdc9af2f (Linux 7.3-rc3 based master);
- correct WK2202 to WK2212 in compatible data and documentation;
- list Huang Yang as the binding and driver maintainer;
- align per-compatible flow-control and RS-485 flags with the product data;
- size DMA-safe SPI buffers independently of cacheline size;
- synchronize TX snapshots with flush without doing SPI under the
  port lock;
- make tx_empty() non-sleeping and maintain its state asynchronously;
- report each FIFO-level RX overrun once;
- clear queued IER configuration during shutdown after cancelling work;
- complete shutdown cleanup on SPI errors and synchronize IRQ/work
  teardown;
- release all serial child-node references;
- remove the arbitrary 200-byte TX cap and replace the 200-iteration poll;
- apply Hugo Villeneuve's naming, comment, whitespace and line-width
  feedback;
- explain why direct SPI and explicit IRQ ownership are retained;
- use WK2204 in the binding example because it enables RS-485.

Conor Dooley's v4 Reviewed-by tag is not carried forward: v5 changes the
compatible and binding maintainer. Please review the updated binding.

Validation performed for the candidate:

- ARM (multi_v7_defconfig, module), ARM64 (defconfig, module and built-in),
  and m68k (multi_defconfig, module) driver builds pass;
- dt_binding_check passes and compiles the binding example; optional
  yamllint was skipped because it is not installed;
- checkpatch reports no errors or checks; patch 2 has one generic warning
  that MAINTAINERS may need updating, and patch 1 adds Huang Yang;
- sparse was not completed because the available sparse 0.6.4 does not support
  the __typeof_unqual__ probe required by this kernel version;
- on the SBC2300/WK2204 CM4 profile, all four ports registered and pairwise
  loopback passed byte-for-byte at 9600, 115200 and 230400 baud;
- the shutdown cleanup passed a four-port 512-byte bidirectional smoke test
  in 10/10 runs on a matched overlay and 3/3 runs after reboot with
  the formal v5 overlay;
- on the v5 candidate, three closed-port module unload/reload cycles and
  post-reload loopback passed;
- on the IPC1200/WK2132 CM4 profile, boot and TX smoke tests passed.

The hardware checks above were performed on Raspberry Pi CM4 systems
running 6.18.34 and 6.18.39 downstream kernels. RS-485 electrical behavior
was not tested.

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 +
 MAINTAINERS                                   |    7 +
 drivers/tty/serial/Kconfig                    |   17 +
 drivers/tty/serial/Makefile                   |    1 +
 drivers/tty/serial/wk2xxx.c                   | 1527 +++++++++++++++++
 include/uapi/linux/serial_core.h              |    3 +
 7 files changed, 1676 insertions(+)
 create mode 100644 Documentation/devicetree/bindings/serial/wkmic,wk2124.yaml
 create mode 100644 drivers/tty/serial/wk2xxx.c

base-commit: 9b87fdc9af2fbfcdb5c24a64139685ef80f6573f

-- 
2.43.0