The MU860 UART does not fully conform to PORT_16650V2 or any other
standard UART configuration. This patch introduces a new UART type,
PORT_MU860, to accurately reflect the hardware characteristics of
MU860-based devices.

The new configuration is applied to Moxa UPCI serial boards to ensure
correct initialization and operation.

Signed-off-by: Crescent Hsieh <crescentcy.hsieh@moxa.com>
---
 drivers/tty/serial/8250/8250_mxupci.c | 3 ++-
 drivers/tty/serial/8250/8250_port.c   | 8 ++++++++
 include/uapi/linux/serial_core.h      | 3 +++
 3 files changed, 13 insertions(+), 1 deletion(-)

diff --git a/drivers/tty/serial/8250/8250_mxupci.c b/drivers/tty/serial/8250/8250_mxupci.c
index fe899ff090c4..d7a4b838ec1f 100644
--- a/drivers/tty/serial/8250/8250_mxupci.c
+++ b/drivers/tty/serial/8250/8250_mxupci.c
@@ -87,7 +87,8 @@ static int mxupci8250_probe(struct pci_dev *pdev, const struct pci_device_id *id
 	up.port.dev = &pdev->dev;
 	up.port.irq = pdev->irq;
 	up.port.uartclk = MOXA_UART_BASE_BAUD * 16;
-	up.port.flags = UPF_SKIP_TEST | UPF_BOOT_AUTOCONF | UPF_SHARE_IRQ;
+	up.port.flags = UPF_SKIP_TEST | UPF_BOOT_AUTOCONF | UPF_SHARE_IRQ | UPF_FIXED_TYPE;
+	up.port.type = PORT_MU860;
 
 	for (i = 0; i < num_ports; i++) {
 		if (serial8250_pci_setup_port(pdev, &up, FL_GET_BASE(FL_BASE2), i * MOXA_UART_OFFSET, 0))
diff --git a/drivers/tty/serial/8250/8250_port.c b/drivers/tty/serial/8250/8250_port.c
index 649e74e9b52f..7d022315b3aa 100644
--- a/drivers/tty/serial/8250/8250_port.c
+++ b/drivers/tty/serial/8250/8250_port.c
@@ -319,6 +319,14 @@ static const struct serial8250_config uart_config[] = {
 		.rxtrig_bytes	= {1, 8, 16, 30},
 		.flags		= UART_CAP_FIFO | UART_CAP_AFE,
 	},
+	[PORT_MU860] = {
+		.name		= "Moxa MU860 UART",
+		.fifo_size	= 128,
+		.tx_loadsz	= 128,
+		.fcr		= UART_FCR_ENABLE_FIFO | UART_FCR_R_TRIG_00,
+		.rxtrig_bytes	= {1, 4, 8, 14},
+		.flags		= UART_CAP_FIFO,
+	},
 };
 
 /* Uart divisor latch read */
diff --git a/include/uapi/linux/serial_core.h b/include/uapi/linux/serial_core.h
index 9c007a106330..49c2fcb2e24c 100644
--- a/include/uapi/linux/serial_core.h
+++ b/include/uapi/linux/serial_core.h
@@ -100,6 +100,9 @@
 /* TXX9 type number */
 #define PORT_TXX9	64
 
+/* Moxa MU860 UART */
+#define PORT_MU860      65
+
 /*Digi jsm */
 #define PORT_JSM        69
 
-- 
2.45.2

On Sun, Nov 30, 2025 at 12:43 PM Crescent Hsieh
<crescentcy.hsieh@moxa.com> wrote:
>
> The MU860 UART does not fully conform to PORT_16650V2 or any other

What are the differences? This list should justify the need for the new type.

> standard UART configuration. This patch introduces a new UART type,

Imperative voice as suggested by Submitting Patch documentation.

> PORT_MU860, to accurately reflect the hardware characteristics of
> MU860-based devices.
>
> The new configuration is applied to Moxa UPCI serial boards to ensure
> correct initialization and operation.

-- 
With Best Regards,
Andy Shevchenko