linux-kernel - [PATCH 2/2] serial: 8250_men_mcb: Parameter for base clockrate

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Message-ID: <20251210164804.94801-3-dev-Felipe.Jensen@duagon.com>
Date: Wed, 10 Dec 2025 17:48:04 +0100
From: Filip Jensen <dev-Felipe.Jensen@...gon.com>
To: gregkh@...uxfoundation.org,
	jirislaby@...nel.org
CC: linux-kernel@...r.kernel.org,
	linux-serial@...r.kernel.org,
	Filip Jensen <dev-Felipe.Jensen@...gon.com>,
	Jose Javier Rodriguez Barbarin <dev-josejavier.rodriguez@...gon.com>
Subject: [PATCH 2/2] serial: 8250_men_mcb: Parameter for base clockrate

A parameter is needed for allowing to change the base clockrate for
each uart port, as this fpga units have no fixed base clock. If the
parameter is not set or is set to 0, it will use the default value.
Allows setting the clockrate up to 64 UARTs.

Reviewed-by: Jose Javier Rodriguez Barbarin <dev-josejavier.rodriguez@...gon.com>
Signed-off-by: Filip Jensen <dev-Felipe.Jensen@...gon.com>
---
 drivers/tty/serial/8250/8250_men_mcb.c | 16 +++++++++++++---
 1 file changed, 13 insertions(+), 3 deletions(-)

diff --git a/drivers/tty/serial/8250/8250_men_mcb.c b/drivers/tty/serial/8250/8250_men_mcb.c
index 6ba7464bb2dd..01dcb9c17b0c 100644
--- a/drivers/tty/serial/8250/8250_men_mcb.c
+++ b/drivers/tty/serial/8250/8250_men_mcb.c
@@ -28,6 +28,7 @@
 #define MEN_UART3_MASK	0x04
 #define MEN_UART4_MASK	0x08
 
+#define MEN_8250_MAX_SETUP		64
 #define MEN_Z025_MAX_UARTS		4
 #define MEN_UART_MEM_SIZE		0x10
 #define MEM_UART_REGISTER_SIZE		0x01
@@ -45,12 +46,18 @@ struct serial_8250_men_mcb_data {
 	int line[MEN_Z025_MAX_UARTS];
 	unsigned int offset[MEN_Z025_MAX_UARTS];
 };
+static int portindex;
+static ulong uartclk[MEN_8250_MAX_SETUP];
+module_param_array(uartclk, ulong, NULL, 0664);
+MODULE_PARM_DESC(
+	uartclk,
+	"Base for baudrate generation for each port. E.g.: uartclk=1843200,1843200,1041666,1041666. If set to 0 it will use board's default");
 
 /*
  * The Z125 16550-compatible UART has no fixed base clock assigned
  * So, depending on the board we're on, we need to adjust the
- * parameter in order to really set the correct baudrate, and
- * do so if possible without user interaction
+ * parameter in order to really set the correct baudrate. Can be
+ * overridden with uartclk parameter.
  */
 static u32 men_lookup_uartclk(struct mcb_device *mdev)
 {
@@ -60,7 +67,9 @@ static u32 men_lookup_uartclk(struct mcb_device *mdev)
 	dev_info(&mdev->dev, "%s on board %s\n",
 		dev_name(&mdev->dev),
 		mdev->bus->name);
-	if  (strncmp(mdev->bus->name, "F075", 4) == 0)
+	if (portindex < MEN_8250_MAX_SETUP && uartclk[portindex])
+		clkval = uartclk[portindex];
+	else if (strncmp(mdev->bus->name, "F075", 4) == 0)
 		clkval = 1041666;
 	else if (strncmp(mdev->bus->name, "F216", 4) == 0)
 		clkval = 1843200;
@@ -72,6 +81,7 @@ static u32 men_lookup_uartclk(struct mcb_device *mdev)
 		dev_info(&mdev->dev,
 			 "board not detected, using default uartclk\n");
 
+	++portindex;
 	clkval = clkval  << 4;
 
 	return clkval;
-- 
2.34.1