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serial: max310x: Setup baud rate generator more precisely

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This patch provide more precisely setup of baud rate generator.
If the result of division has a remainder, we use the multiplier
for the base frequency. Additionally, we report result baud rate
back to serial core.

Signed-off-by: Alexander Shiyan <shc_work@mail.ru>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
This commit is contained in:
Alexander Shiyan 2014-02-07 18:16:04 +04:00 committed by Greg Kroah-Hartman
parent d0fd413cff
commit e97e15561c
1 changed files with 19 additions and 11 deletions
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30
drivers/tty/serial/max310x.c
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@ -1,7 +1,7 @@
/*
* Maxim (Dallas) MAX3107/8/9, MAX14830 serial driver
*
* Copyright (C) 2012-2013 Alexander Shiyan <shc_work@mail.ru>
* Copyright (C) 2012-2014 Alexander Shiyan <shc_work@mail.ru>
*
* Based on max3100.c, by Christian Pellegrin <chripell@evolware.org>
* Based on max3110.c, by Feng Tang <feng.tang@intel.com>
@ -504,25 +504,33 @@ static bool max310x_reg_precious(struct device *dev, unsigned int reg)
return false;
}
static void max310x_set_baud(struct uart_port *port, int baud)
static int max310x_set_baud(struct uart_port *port, int baud)
{
unsigned int mode = 0, div = port->uartclk / baud;
unsigned int mode = 0, clk = port->uartclk, div = clk / baud;
if (!(div / 16)) {
/* Check for minimal value for divider */
if (div < 16)
div = 16;
if (clk % baud && (div / 16) < 0x8000) {
/* Mode x2 */
mode = MAX310X_BRGCFG_2XMODE_BIT;
div = (port->uartclk * 2) / baud;
}
clk = port->uartclk * 2;
div = clk / baud;
if (!(div / 16)) {
/* Mode x4 */
mode = MAX310X_BRGCFG_4XMODE_BIT;
div = (port->uartclk * 4) / baud;
if (clk % baud && (div / 16) < 0x8000) {
/* Mode x4 */
mode = MAX310X_BRGCFG_4XMODE_BIT;
clk = port->uartclk * 4;
div = clk / baud;
}
}
max310x_port_write(port, MAX310X_BRGDIVMSB_REG, (div / 16) >> 8);
max310x_port_write(port, MAX310X_BRGDIVLSB_REG, div / 16);
max310x_port_write(port, MAX310X_BRGCFG_REG, (div % 16) | mode);
return DIV_ROUND_CLOSEST(clk, div);
}
static int max310x_update_best_err(unsigned long f, long *besterr)
@ -875,7 +883,7 @@ static void max310x_set_termios(struct uart_port *port,
port->uartclk / 4);
/* Setup baudrate generator */
max310x_set_baud(port, baud);
baud = max310x_set_baud(port, baud);
/* Update timeout according to new baud rate */
uart_update_timeout(port, termios->c_cflag, baud);