diff --git a/drivers/tty/serial/max310x.c b/drivers/tty/serial/max310x.c index 0e3dc89c459b..ca044f96c5cc 100644 --- a/drivers/tty/serial/max310x.c +++ b/drivers/tty/serial/max310x.c @@ -501,37 +501,48 @@ static bool max310x_reg_precious(struct device *dev, unsigned int reg) static int max310x_set_baud(struct uart_port *port, int baud) { - unsigned int mode = 0, clk = port->uartclk, div = clk / baud; + unsigned int mode = 0, div = 0, frac = 0, c = 0, F = 0; - /* Check for minimal value for divider */ - if (div < 16) - div = 16; - - if (clk % baud && (div / 16) < 0x8000) { + /* + * Calculate the integer divisor first. Select a proper mode + * in case if the requested baud is too high for the pre-defined + * clocks frequency. + */ + div = port->uartclk / baud; + if (div < 8) { + /* Mode x4 */ + c = 4; + mode = MAX310X_BRGCFG_4XMODE_BIT; + } else if (div < 16) { /* Mode x2 */ + c = 8; mode = MAX310X_BRGCFG_2XMODE_BIT; - clk = port->uartclk * 2; - div = clk / baud; - - if (clk % baud && (div / 16) < 0x8000) { - /* Mode x4 */ - mode = MAX310X_BRGCFG_4XMODE_BIT; - clk = port->uartclk * 4; - div = clk / baud; - } + } else { + c = 16; } - 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); + /* Calculate the divisor in accordance with the fraction coefficient */ + div /= c; + F = c*baud; - return DIV_ROUND_CLOSEST(clk, div); + /* Calculate the baud rate fraction */ + if (div > 0) + frac = (16*(port->uartclk % F)) / F; + else + div = 1; + + max310x_port_write(port, MAX310X_BRGDIVMSB_REG, div >> 8); + max310x_port_write(port, MAX310X_BRGDIVLSB_REG, div); + max310x_port_write(port, MAX310X_BRGCFG_REG, frac | mode); + + /* Return the actual baud rate we just programmed */ + return (16*port->uartclk) / (c*(16*div + frac)); } static int max310x_update_best_err(unsigned long f, long *besterr) { /* Use baudrate 115200 for calculate error */ - long err = f % (115200 * 16); + long err = f % (460800 * 16); if ((*besterr < 0) || (*besterr > err)) { *besterr = err;