linux-kernel - [PATCH 2/3] tty: serial: meson: Added 12Mhz as the clock source for calculating baud rate

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Message-ID: <20220407081355.13602-3-yu.tu@amlogic.com>
Date:   Thu, 7 Apr 2022 16:13:54 +0800
From:   Yu Tu <yu.tu@...ogic.com>
To:     <linux-serial@...r.kernel.org>,
        <linux-arm-kernel@...ts.infradead.org>,
        <linux-amlogic@...ts.infradead.org>,
        <linux-kernel@...r.kernel.org>,
        Neil Armstrong <narmstrong@...libre.com>,
        Kevin Hilman <khilman@...libre.com>,
        Jerome Brunet <jbrunet@...libre.com>
CC:     Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        Jiri Slaby <jirislaby@...nel.org>,
        Martin Blumenstingl <martin.blumenstingl@...glemail.com>,
        Yu Tu <yu.tu@...ogic.com>
Subject: [PATCH 2/3] tty: serial: meson: Added 12Mhz as the clock source for calculating baud rate

Starting with the g12A chip, add a 12Mhz clock to calculate the baud
rate, since the BT module uses 3Mhz baud rate. 8Mhz calculations can
lead to baud rate bias, causing some problems.

Signed-off-by: Yu Tu <yu.tu@...ogic.com>
---
 drivers/tty/serial/meson_uart.c | 25 +++++++++++++++++++++++--
 1 file changed, 23 insertions(+), 2 deletions(-)

diff --git a/drivers/tty/serial/meson_uart.c b/drivers/tty/serial/meson_uart.c
index 8e59624935af..7e77693a1318 100644
--- a/drivers/tty/serial/meson_uart.c
+++ b/drivers/tty/serial/meson_uart.c
@@ -68,6 +68,7 @@
 #define AML_UART_BAUD_MASK		0x7fffff
 #define AML_UART_BAUD_USE		BIT(23)
 #define AML_UART_BAUD_XTAL		BIT(24)
+#define AML_UART_BAUD_XTAL_DIV2		BIT(27)
 
 #define AML_UART_PORT_NUM		12
 #define AML_UART_PORT_OFFSET		6
@@ -80,6 +81,10 @@ static struct uart_driver meson_uart_driver;
 
 static struct uart_port *meson_ports[AML_UART_PORT_NUM];
 
+struct meson_uart_data {
+	bool has_xtal_div2;
+};
+
 static void meson_uart_set_mctrl(struct uart_port *port, unsigned int mctrl)
 {
 }
@@ -293,13 +298,20 @@ static int meson_uart_startup(struct uart_port *port)
 
 static void meson_uart_change_speed(struct uart_port *port, unsigned long baud)
 {
-	u32 val;
+	struct meson_uart_data *private_data = port->private_data;
+	u32 val = 0;
 
 	while (!meson_uart_tx_empty(port))
 		cpu_relax();
 
 	if (port->uartclk == 24000000) {
-		val = DIV_ROUND_CLOSEST(port->uartclk / 3, baud) - 1;
+		unsigned int xtal_div = 3;
+
+		if (private_data->has_xtal_div2) {
+			xtal_div = 2;
+			val |= AML_UART_BAUD_XTAL_DIV2;
+		}
+		val |= DIV_ROUND_CLOSEST(port->uartclk / xtal_div, baud) - 1;
 		val |= AML_UART_BAUD_XTAL;
 	} else {
 		val =  DIV_ROUND_CLOSEST(port->uartclk / 4, baud) - 1;
@@ -691,6 +703,7 @@ static int meson_uart_probe_clocks(struct platform_device *pdev,
 
 static int meson_uart_probe(struct platform_device *pdev)
 {
+	struct meson_uart_data *private_data;
 	struct resource *res_mem;
 	struct uart_port *port;
 	u32 fifosize = 64; /* Default is 64, 128 for EE UART_0 */
@@ -733,6 +746,13 @@ static int meson_uart_probe(struct platform_device *pdev)
 	if (!port)
 		return -ENOMEM;
 
+	private_data = devm_kzalloc(&pdev->dev, sizeof(struct meson_uart_data), GFP_KERNEL);
+	if (!private_data)
+		return -ENOMEM;
+
+	if ((bool)device_get_match_data(&pdev->dev))
+		private_data->has_xtal_div2 = true;
+
 	ret = meson_uart_probe_clocks(pdev, port);
 	if (ret)
 		return ret;
@@ -749,6 +769,7 @@ static int meson_uart_probe(struct platform_device *pdev)
 	port->x_char = 0;
 	port->ops = &meson_uart_ops;
 	port->fifosize = fifosize;
+	port->private_data = private_data;
 
 	meson_ports[pdev->id] = port;
 	platform_set_drvdata(pdev, port);
-- 
2.33.1