[07/16] serial: mvebu-uart: add function to change baudrate

Message ID 20171006101344.15590-8-miquel.raynal@free-electrons.com
State New
Headers show
Series
  • Support armada-37xx second UART port
Related show

Commit Message

Miquel RAYNAL Oct. 6, 2017, 10:13 a.m.
From: Allen Yan <yanwei@marvell.com>

Until now, the first UART port baudrate was set by the bootloader.

Add a function allowing to change the baudrate. Changes may be done
from userspace but also at probe time by the kernel. Use the simplest
method: baudrate divisor.

Works for all UART ports until 230400 baud. To achieve higher baudrates,
software should implement the fractional divisor feature that allows
more accuracy for higher rates.

Signed-off-by: Allen Yan <yanwei@marvell.com>
[<miquel.raynal@free-electrons.com>: changed termios handling]
Signed-off-by: Miquel Raynal <miquel.raynal@free-electrons.com>
---
 drivers/tty/serial/mvebu-uart.c | 69 ++++++++++++++++++++++++++++++++++++++---
 1 file changed, 65 insertions(+), 4 deletions(-)

Comments

Gregory CLEMENT Oct. 6, 2017, 12:39 p.m. | #1
Hi Miquel,
 
 On ven., oct. 06 2017, Miquel Raynal <miquel.raynal@free-electrons.com> wrote:

> From: Allen Yan <yanwei@marvell.com>
>
> Until now, the first UART port baudrate was set by the bootloader.
>
> Add a function allowing to change the baudrate. Changes may be done
> from userspace but also at probe time by the kernel. Use the simplest
> method: baudrate divisor.
>
> Works for all UART ports until 230400 baud. To achieve higher baudrates,
> software should implement the fractional divisor feature that allows
> more accuracy for higher rates.
>
> Signed-off-by: Allen Yan <yanwei@marvell.com>
> [<miquel.raynal@free-electrons.com>: changed termios handling]
> Signed-off-by: Miquel Raynal <miquel.raynal@free-electrons.com>

Reviewed-by: Gregory CLEMENT <gregory.clement@free-electrons.com>

Thanks,

Gregory


> ---
>  drivers/tty/serial/mvebu-uart.c | 69 ++++++++++++++++++++++++++++++++++++++---
>  1 file changed, 65 insertions(+), 4 deletions(-)
>
> diff --git a/drivers/tty/serial/mvebu-uart.c b/drivers/tty/serial/mvebu-uart.c
> index da756cfec0bb..81a3d2714fd3 100644
> --- a/drivers/tty/serial/mvebu-uart.c
> +++ b/drivers/tty/serial/mvebu-uart.c
> @@ -72,6 +72,7 @@
>  				 | STAT_PAR_ERR | STAT_OVR_ERR)
>  
>  #define UART_BRDV		0x10
> +#define  BRDV_BAUD_MASK         0x3FF
>  
>  #define MVEBU_NR_UARTS		1
>  
> @@ -344,6 +345,31 @@ static void mvebu_uart_shutdown(struct uart_port *port)
>  	free_irq(port->irq, port);
>  }
>  
> +static int mvebu_uart_baud_rate_set(struct uart_port *port, unsigned int baud)
> +{
> +	struct mvebu_uart *mvuart = to_mvuart(port);
> +	unsigned int baud_rate_div;
> +	u32 brdv;
> +
> +	if (IS_ERR(mvuart->clk))
> +		return -PTR_ERR(mvuart->clk);
> +
> +	/*
> +	 * The UART clock is divided by the value of the divisor to generate
> +	 * UCLK_OUT clock, which is 16 times faster than the baudrate.
> +	 * This prescaler can achieve all standard baudrates until 230400.
> +	 * Higher baudrates could be achieved for the extended UART by using the
> +	 * programmable oversampling stack (also called fractional divisor).
> +	 */
> +	baud_rate_div = DIV_ROUND_UP(port->uartclk, baud * 16);
> +	brdv = readl(port->membase + UART_BRDV);
> +	brdv &= ~BRDV_BAUD_MASK;
> +	brdv |= baud_rate_div;
> +	writel(brdv, port->membase + UART_BRDV);
> +
> +	return 0;
> +}
> +
>  static void mvebu_uart_set_termios(struct uart_port *port,
>  				   struct ktermios *termios,
>  				   struct ktermios *old)
> @@ -367,11 +393,30 @@ static void mvebu_uart_set_termios(struct uart_port *port,
>  	if ((termios->c_cflag & CREAD) == 0)
>  		port->ignore_status_mask |= STAT_RX_RDY(port) | STAT_BRK_ERR;
>  
> -	if (old)
> -		tty_termios_copy_hw(termios, old);
> +	/*
> +	 * Maximum achievable frequency with simple baudrate divisor is 230400.
> +	 * Since the error per bit frame would be of more than 15%, achieving
> +	 * higher frequencies would require to implement the fractional divisor
> +	 * feature.
> +	 */
> +	baud = uart_get_baud_rate(port, termios, old, 0, 230400);
> +	if (mvebu_uart_baud_rate_set(port, baud)) {
> +		/* No clock available, baudrate cannot be changed */
> +		if (old)
> +			baud = uart_get_baud_rate(port, old, NULL, 0, 230400);
> +	} else {
> +		tty_termios_encode_baud_rate(termios, baud, baud);
> +		uart_update_timeout(port, termios->c_cflag, baud);
> +	}
>  
> -	baud = uart_get_baud_rate(port, termios, old, 0, 460800);
> -	uart_update_timeout(port, termios->c_cflag, baud);
> +	/* Only the following flag changes are supported */
> +	if (old) {
> +		termios->c_iflag &= INPCK | IGNPAR;
> +		termios->c_iflag |= old->c_iflag & ~(INPCK | IGNPAR);
> +		termios->c_cflag &= CREAD | CBAUD;
> +		termios->c_cflag |= old->c_cflag & ~(CREAD | CBAUD);
> +		termios->c_lflag = old->c_lflag;
> +	}
>  
>  	spin_unlock_irqrestore(&port->lock, flags);
>  }
> @@ -647,12 +692,28 @@ static int mvebu_uart_probe(struct platform_device *pdev)
>  	if (!mvuart)
>  		return -ENOMEM;
>  
> +	/* Get controller data depending on the compatible string */
>  	mvuart->data = (struct mvebu_uart_driver_data *)match->data;
>  	mvuart->port = port;
>  
>  	port->private_data = mvuart;
>  	platform_set_drvdata(pdev, mvuart);
>  
> +	/* Get fixed clock frequency */
> +	mvuart->clk = devm_clk_get(&pdev->dev, NULL);
> +	if (IS_ERR(mvuart->clk)) {
> +		if (PTR_ERR(mvuart->clk) == -EPROBE_DEFER)
> +			return PTR_ERR(mvuart->clk);
> +
> +		if (IS_EXTENDED(port)) {
> +			dev_err(&pdev->dev, "unable to get UART clock\n");
> +			return PTR_ERR(mvuart->clk);
> +		}
> +	} else {
> +		if (!clk_prepare_enable(mvuart->clk))
> +			port->uartclk = clk_get_rate(mvuart->clk);
> +	}
> +
>  	/* UART Soft Reset*/
>  	writel(CTRL_SOFT_RST, port->membase + UART_CTRL(port));
>  	udelay(1);
> -- 
> 2.11.0
>
>
> _______________________________________________
> linux-arm-kernel mailing list
> linux-arm-kernel@lists.infradead.org
> http://lists.infradead.org/mailman/listinfo/linux-arm-kernel

Patch

diff --git a/drivers/tty/serial/mvebu-uart.c b/drivers/tty/serial/mvebu-uart.c
index da756cfec0bb..81a3d2714fd3 100644
--- a/drivers/tty/serial/mvebu-uart.c
+++ b/drivers/tty/serial/mvebu-uart.c
@@ -72,6 +72,7 @@ 
 				 | STAT_PAR_ERR | STAT_OVR_ERR)
 
 #define UART_BRDV		0x10
+#define  BRDV_BAUD_MASK         0x3FF
 
 #define MVEBU_NR_UARTS		1
 
@@ -344,6 +345,31 @@  static void mvebu_uart_shutdown(struct uart_port *port)
 	free_irq(port->irq, port);
 }
 
+static int mvebu_uart_baud_rate_set(struct uart_port *port, unsigned int baud)
+{
+	struct mvebu_uart *mvuart = to_mvuart(port);
+	unsigned int baud_rate_div;
+	u32 brdv;
+
+	if (IS_ERR(mvuart->clk))
+		return -PTR_ERR(mvuart->clk);
+
+	/*
+	 * The UART clock is divided by the value of the divisor to generate
+	 * UCLK_OUT clock, which is 16 times faster than the baudrate.
+	 * This prescaler can achieve all standard baudrates until 230400.
+	 * Higher baudrates could be achieved for the extended UART by using the
+	 * programmable oversampling stack (also called fractional divisor).
+	 */
+	baud_rate_div = DIV_ROUND_UP(port->uartclk, baud * 16);
+	brdv = readl(port->membase + UART_BRDV);
+	brdv &= ~BRDV_BAUD_MASK;
+	brdv |= baud_rate_div;
+	writel(brdv, port->membase + UART_BRDV);
+
+	return 0;
+}
+
 static void mvebu_uart_set_termios(struct uart_port *port,
 				   struct ktermios *termios,
 				   struct ktermios *old)
@@ -367,11 +393,30 @@  static void mvebu_uart_set_termios(struct uart_port *port,
 	if ((termios->c_cflag & CREAD) == 0)
 		port->ignore_status_mask |= STAT_RX_RDY(port) | STAT_BRK_ERR;
 
-	if (old)
-		tty_termios_copy_hw(termios, old);
+	/*
+	 * Maximum achievable frequency with simple baudrate divisor is 230400.
+	 * Since the error per bit frame would be of more than 15%, achieving
+	 * higher frequencies would require to implement the fractional divisor
+	 * feature.
+	 */
+	baud = uart_get_baud_rate(port, termios, old, 0, 230400);
+	if (mvebu_uart_baud_rate_set(port, baud)) {
+		/* No clock available, baudrate cannot be changed */
+		if (old)
+			baud = uart_get_baud_rate(port, old, NULL, 0, 230400);
+	} else {
+		tty_termios_encode_baud_rate(termios, baud, baud);
+		uart_update_timeout(port, termios->c_cflag, baud);
+	}
 
-	baud = uart_get_baud_rate(port, termios, old, 0, 460800);
-	uart_update_timeout(port, termios->c_cflag, baud);
+	/* Only the following flag changes are supported */
+	if (old) {
+		termios->c_iflag &= INPCK | IGNPAR;
+		termios->c_iflag |= old->c_iflag & ~(INPCK | IGNPAR);
+		termios->c_cflag &= CREAD | CBAUD;
+		termios->c_cflag |= old->c_cflag & ~(CREAD | CBAUD);
+		termios->c_lflag = old->c_lflag;
+	}
 
 	spin_unlock_irqrestore(&port->lock, flags);
 }
@@ -647,12 +692,28 @@  static int mvebu_uart_probe(struct platform_device *pdev)
 	if (!mvuart)
 		return -ENOMEM;
 
+	/* Get controller data depending on the compatible string */
 	mvuart->data = (struct mvebu_uart_driver_data *)match->data;
 	mvuart->port = port;
 
 	port->private_data = mvuart;
 	platform_set_drvdata(pdev, mvuart);
 
+	/* Get fixed clock frequency */
+	mvuart->clk = devm_clk_get(&pdev->dev, NULL);
+	if (IS_ERR(mvuart->clk)) {
+		if (PTR_ERR(mvuart->clk) == -EPROBE_DEFER)
+			return PTR_ERR(mvuart->clk);
+
+		if (IS_EXTENDED(port)) {
+			dev_err(&pdev->dev, "unable to get UART clock\n");
+			return PTR_ERR(mvuart->clk);
+		}
+	} else {
+		if (!clk_prepare_enable(mvuart->clk))
+			port->uartclk = clk_get_rate(mvuart->clk);
+	}
+
 	/* UART Soft Reset*/
 	writel(CTRL_SOFT_RST, port->membase + UART_CTRL(port));
 	udelay(1);