diff options
Diffstat (limited to 'drivers/tty/serial/mvebu-uart.c')
| -rw-r--r-- | drivers/tty/serial/mvebu-uart.c | 29 |
1 files changed, 20 insertions, 9 deletions
diff --git a/drivers/tty/serial/mvebu-uart.c b/drivers/tty/serial/mvebu-uart.c index 170e446a2f62..231f751d1ef4 100644 --- a/drivers/tty/serial/mvebu-uart.c +++ b/drivers/tty/serial/mvebu-uart.c @@ -72,6 +72,8 @@ #define BRDV_BAUD_MASK 0x3FF #define UART_OSAMP 0x14 +#define OSAMP_DEFAULT_DIVISOR 16 +#define OSAMP_DIVISORS_MASK 0x3F3F3F3F #define MVEBU_NR_UARTS 2 @@ -444,25 +446,34 @@ static void mvebu_uart_shutdown(struct uart_port *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; + unsigned int d_divisor, m_divisor; + u32 brdv, osamp; 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). + * The baudrate is derived from the UART clock thanks to two divisors: + * > D ("baud generator"): can divide the clock from 2 to 2^10 - 1. + * > M ("fractional divisor"): allows a better accuracy for + * baudrates higher than 230400. + * + * As the derivation of M is rather complicated, the code sticks to its + * default value (x16) when all the prescalers are zeroed, and only + * makes use of D to configure the desired baudrate. */ - baud_rate_div = DIV_ROUND_UP(port->uartclk, baud * 16); + m_divisor = OSAMP_DEFAULT_DIVISOR; + d_divisor = DIV_ROUND_UP(port->uartclk, baud * m_divisor); + brdv = readl(port->membase + UART_BRDV); brdv &= ~BRDV_BAUD_MASK; - brdv |= baud_rate_div; + brdv |= d_divisor; writel(brdv, port->membase + UART_BRDV); + osamp = readl(port->membase + UART_OSAMP); + osamp &= ~OSAMP_DIVISORS_MASK; + writel(osamp, port->membase + UART_OSAMP); + return 0; } |