[PATCH v2 0/2] serial: 8250: loongson: Add support for MIPS-based Loongson 3A4000

[Rong Zhang]

This series targets the serial tree.

The UART controller on Loongson 3A4000 is compatible with Loongson
2K1500, which is NS16550A-compatible with an additional fractional
frequency divisor register.

Patch 1 adds loongson,ls3a4000-uart as compatible with
loongson,ls2k1500-uart.

Patch 2 enables building 8250_loongson (loongson-uart) on MIPS
Loongson64.

Tested on Loongson-LS3A4000-7A1000-NUC-SE with a 25MHz UART clock.
Without fractional frequency divisor, the actual baud rate was 111607
(25MHz / 16 / 14, measured value: 111545) and some USB-to-UART
converters couldn't work with it at all. With fractional frequency
divisor, the measured baud rate becomes 115207, which is quite accurate.

The patch for the MIPS tree to update the compatible strings in the
loongson64g-package DTS is sent separately, as it's independant of this
series and can be applied in any order (the compatible strings there
still contain "ns16550a", so no regression will be introduced).

Changes in v2:
- Separated from v1 (patch 1,2): https://lore.kernel.org/r/20260314234143.651298-1-rongrong@xxxxxxxxxxxxxxxxx/
(thanks Krzysztof Kozlowski)

Rong Zhang (2):
  dt-bindings: serial: 8250: Add Loongson 3A4000 uart compatible
  serial: 8250: loongson: Enable building on MIPS Loongson64

 Documentation/devicetree/bindings/serial/8250.yaml | 1 +
 drivers/tty/serial/8250/Kconfig                    | 9 +++++----
 2 files changed, 6 insertions(+), 4 deletions(-)


base-commit: 267594792a71018788af69e836c52e34bb8054af
-- 
2.53.0