uart: Introduce uart driver for the Loongson family

Hi all:

For various reasons, I will be taking over from Haowei and continuing to push forward with this patch set. Thanks to Haowei for his efforts so far.

This patchset introduce a generic UART framework driver for Loongson family. It can be found on Loongson3 series cpus, Loongson-2K series cpus and Loongson LS7A bridge chips.

Thanks.

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V6:
Patch-1:
- Add Conor's Acked-by tag, thanks.

Patch-2:
- Add more missing #include;
- Convert mcr_invert/msr_invert from int to u8;
- Split serial_fixup() on a preceding line;
- Add macro definition to avoid magic numbers, such as LOONGSON_QUOT_FRAC_MASK;
- Rework the relevant data structures, where loongson_uart_ddata represents the Soc's driver_data;
- Drop PORT_LOONGSON and use PORT_16550A instead.
- devm_platform_get_and_ioremap_resource() instead of platform_get_resource();
- Use uart_read_port_properties() and parse the clock attributes;
- Use switch-case instead of if-else in serial_fixup().

Link to V5:
https://lore.kernel.org/all/[email protected]/

V5:
Patch-1:
- Since the Loongson UART is NS8250A-compatible, simply add ls2k* compatible to 8250.yaml.

DTS{i} tested by make dtbs_check W=1

Link to V4:
https://lore.kernel.org/all/[email protected]/

V4:
Patch-1:
- Rename binding name from loongson,uart.yaml to

    loongson,ls2k0500-uart.yaml;

- Drop ls7a compatible;
- According to the manual, ls3a and ls2k uart are the same, so merge their compatible.

Patch-2:
- Format code;
- Add the LOONGSON_UART_DLF macro definition to avoid magic numbers;
- Simplify the code, merge flags and quirks, and remove struct

    loongson_uart_config;

- Use DEFINE_SIMPLE_DEV_PM_OPS;
- Drop loongson,ls7a-uart compatible.

Patch-3:
- Add ls2k* compatible string, and ns16550a as the fallback compatible.

Link to V3:
https://lore.kernel.org/all/[email protected]/

Binbin Zhou (3):
dt-bindings: serial: 8250: Add Loongson uart compatible
serial: 8250: Add Loongson uart driver support
LoongArch: dts: Add uart new compatible string

 .../devicetree/bindings/serial/8250.yaml      |  14 ++
 arch/loongarch/boot/dts/loongson-2k0500.dtsi  |   2 +-
 arch/loongarch/boot/dts/loongson-2k1000.dtsi  |   2 +-
 arch/loongarch/boot/dts/loongson-2k2000.dtsi  |   2 +-
 drivers/tty/serial/8250/8250_loongson.c       | 238 ++++++++++++++++++
 drivers/tty/serial/8250/Kconfig               |  10 +
 drivers/tty/serial/8250/Makefile              |   1 +
 7 files changed, 266 insertions(+), 3 deletions(-)
 create mode 100644 drivers/tty/serial/8250/8250_loongson.c

base-commit: 0d97f2067c166eb495771fede9f7b73999c67f66

2.47.3