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serial: mvebu-uart: add function to change baudrate

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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>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
This commit is contained in:
Allen Yan 2017-10-13 11:01:51 +02:00 committed by Greg Kroah-Hartman
parent 9c3d3ee123
commit 68a0db1d7d
1 changed files with 65 additions and 4 deletions
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69
drivers/tty/serial/mvebu-uart.c
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@ -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);
}
@ -654,12 +699,28 @@ 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);