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Subject[PATCH V2 1/2] tty: serial: meson: Add a 12MHz internal clock rate to calculate baud rate in order to meet the baud rate requirements of special BT modules
Date
A /2 divider over XTAL was introduced since G12A, and is preferred
to be used over the still present /3 divider since it provides much
closer frequencies vs the request baudrate.Especially 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@amlogic.com>
---
drivers/tty/serial/meson_uart.c | 17 +++++++++++++++--
1 file changed, 15 insertions(+), 2 deletions(-)

diff --git a/drivers/tty/serial/meson_uart.c b/drivers/tty/serial/meson_uart.c
index 8e59624935af..58bd2723c004 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;
+ const 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 && 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;
@@ -749,6 +761,7 @@ static int meson_uart_probe(struct platform_device *pdev)
port->x_char = 0;
port->ops = &meson_uart_ops;
port->fifosize = fifosize;
+ port->private_data = (void *)device_get_match_data(&pdev->dev);

meson_ports[pdev->id] = port;
platform_set_drvdata(pdev, port);
--
2.33.1
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