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

[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@oss.cipunited.com/
(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

[PATCH v2 1/2] dt-bindings: serial: 8250: Add Loongson 3A4000 uart compatible

[Rong Zhang]

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

Add loongson,ls3a4000-uart as compatible with loongson,ls2k1500-uart.

Acked-by: Krzysztof Kozlowski <krzysztof.kozlowski@oss.qualcomm.com>
Signed-off-by: Rong Zhang <rongrong@oss.cipunited.com>
---
 Documentation/devicetree/bindings/serial/8250.yaml | 1 +
 1 file changed, 1 insertion(+)

diff --git a/Documentation/devicetree/bindings/serial/8250.yaml b/Documentation/devicetree/bindings/serial/8250.yaml
index 73851f19330d..1d1f2a22776c 100644
--- a/Documentation/devicetree/bindings/serial/8250.yaml
+++ b/Documentation/devicetree/bindings/serial/8250.yaml
@@ -179,6 +179,7 @@ properties:
           - const: ns16550a
       - items:
           - enum:
+              - loongson,ls3a4000-uart
               - loongson,ls3a5000-uart
               - loongson,ls3a6000-uart
               - loongson,ls2k2000-uart
-- 
2.53.0

[PATCH v2 2/2] serial: 8250: loongson: Enable building on MIPS Loongson64

[Rong Zhang]

Loongson 3A4000 is a MIPS-based Loongson64 CPU which also supports
8250_loongson (loongson-uart).

Enable building on MIPS Loongson64 so that Loongson 3A4000 can benefit
from it.

Signed-off-by: Rong Zhang <rongrong@oss.cipunited.com>
---
 drivers/tty/serial/8250/Kconfig | 9 +++++----
 1 file changed, 5 insertions(+), 4 deletions(-)

diff --git a/drivers/tty/serial/8250/Kconfig b/drivers/tty/serial/8250/Kconfig
index fd4e8b6ab60d..fc3e58d62233 100644
--- a/drivers/tty/serial/8250/Kconfig
+++ b/drivers/tty/serial/8250/Kconfig
@@ -465,11 +465,12 @@ config SERIAL_8250_OMAP_TTYO_FIXUP
 config SERIAL_8250_LOONGSON
 	tristate "Loongson 8250 based serial port"
 	depends on SERIAL_8250
-	depends on LOONGARCH || COMPILE_TEST
+	depends on LOONGARCH || MACH_LOONGSON64 || COMPILE_TEST
 	help
-	  If you have a machine based on LoongArch CPU you can enable
-	  its onboard serial ports by enabling this option. The option
-	  is applicable to both devicetree and ACPI, say Y to this option.
+	  If you have a machine based on LoongArch CPU or MIPS-based Loongson
+	  3A4000 CPU you can enable its onboard serial ports by enabling this
+	  option. The option is applicable to both devicetree and ACPI, say Y
+	  to enable this option.
 	  If unsure, say N.
 
 config SERIAL_8250_LPC18XX
-- 
2.53.0

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

[Jiaxun Yang]

On Sun, 15 Mar 2026, at 6:42 PM, Rong Zhang wrote:
> 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@oss.cipunited.com/
> (thanks Krzysztof Kozlowski)

For the series:

Reviewed-by: Jiaxun Yang <jiaxun.yang@flygoat.com>

Thanks!

>
> 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

-- 
- Jiaxun