Hi Miquel,
On ven., oct. 06 2017, Miquel Raynal <miquel.raynal@xxxxxxxxxxxxxxxxxx> wrote:
> From: Allen Yan <yanwei@xxxxxxxxxxx>
>
> 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@xxxxxxxxxxx>
> [<miquel.raynal@xxxxxxxxxxxxxxxxxx>: changed termios handling]
> Signed-off-by: Miquel Raynal <miquel.raynal@xxxxxxxxxxxxxxxxxx>
Reviewed-by: Gregory CLEMENT <gregory.clement@xxxxxxxxxxxxxxxxxx>
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
>
>
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> linux-arm-kernel@xxxxxxxxxxxxxxxxxxx
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--
Gregory Clement, Free Electrons
Kernel, drivers, real-time and embedded Linux
development, consulting, training and support.
http://free-electrons.com
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