diff options
author | Ludovic Desroches <ludovic.desroches@atmel.com> | 2016-08-25 13:47:56 (GMT) |
---|---|---|
committer | Greg Kroah-Hartman <gregkh@linuxfoundation.org> | 2016-08-31 13:39:58 (GMT) |
commit | 5bf5635ac1705b8d58fdef5ff0666ef0e72b4629 (patch) | |
tree | 3f1aebb7026dd29035806f3ca7e7bad93be8a52d /drivers/tty/serial | |
parent | 2426fbc77faef57c80a573303af6543531e2efa3 (diff) | |
download | linux-5bf5635ac1705b8d58fdef5ff0666ef0e72b4629.tar.xz |
tty/serial: atmel: add fractional baud rate support
The USART device provides a fractional baud rate generator to get a more
accurate baud rate. It can be used only when the USART is configured in
'normal mode' and this feature is not available on AT91RM9200 SoC.
Signed-off-by: Ludovic Desroches <ludovic.desroches@atmel.com>
Acked-by: Nicolas Ferre <nicolas.ferre@atmel.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Diffstat (limited to 'drivers/tty/serial')
-rw-r--r-- | drivers/tty/serial/atmel_serial.c | 41 |
1 files changed, 33 insertions, 8 deletions
diff --git a/drivers/tty/serial/atmel_serial.c b/drivers/tty/serial/atmel_serial.c index 2eaa18d..1759239 100644 --- a/drivers/tty/serial/atmel_serial.c +++ b/drivers/tty/serial/atmel_serial.c @@ -166,6 +166,7 @@ struct atmel_uart_port { u32 rts_low; bool ms_irq_enabled; u32 rtor; /* address of receiver timeout register if it exists */ + bool has_frac_baudrate; bool has_hw_timer; struct timer_list uart_timer; @@ -1745,6 +1746,11 @@ static void atmel_get_ip_name(struct uart_port *port) dbgu_uart = 0x44424755; /* DBGU */ new_uart = 0x55415254; /* UART */ + /* + * Only USART devices from at91sam9260 SOC implement fractional + * baudrate. + */ + atmel_port->has_frac_baudrate = false; atmel_port->has_hw_timer = false; if (name == new_uart) { @@ -1753,6 +1759,7 @@ static void atmel_get_ip_name(struct uart_port *port) atmel_port->rtor = ATMEL_UA_RTOR; } else if (name == usart) { dev_dbg(port->dev, "Usart\n"); + atmel_port->has_frac_baudrate = true; atmel_port->has_hw_timer = true; atmel_port->rtor = ATMEL_US_RTOR; } else if (name == dbgu_uart) { @@ -1764,6 +1771,7 @@ static void atmel_get_ip_name(struct uart_port *port) case 0x302: case 0x10213: dev_dbg(port->dev, "This version is usart\n"); + atmel_port->has_frac_baudrate = true; atmel_port->has_hw_timer = true; atmel_port->rtor = ATMEL_US_RTOR; break; @@ -2025,8 +2033,9 @@ static void atmel_serial_pm(struct uart_port *port, unsigned int state, static void atmel_set_termios(struct uart_port *port, struct ktermios *termios, struct ktermios *old) { + struct atmel_uart_port *atmel_port = to_atmel_uart_port(port); unsigned long flags; - unsigned int old_mode, mode, imr, quot, baud; + unsigned int old_mode, mode, imr, quot, baud, div, cd, fp = 0; /* save the current mode register */ mode = old_mode = atmel_uart_readl(port, ATMEL_US_MR); @@ -2036,12 +2045,6 @@ static void atmel_set_termios(struct uart_port *port, struct ktermios *termios, ATMEL_US_PAR | ATMEL_US_USMODE); baud = uart_get_baud_rate(port, termios, old, 0, port->uartclk / 16); - quot = uart_get_divisor(port, baud); - - if (quot > 65535) { /* BRGR is 16-bit, so switch to slower clock */ - quot /= 8; - mode |= ATMEL_US_USCLKS_MCK_DIV8; - } /* byte size */ switch (termios->c_cflag & CSIZE) { @@ -2160,7 +2163,29 @@ static void atmel_set_termios(struct uart_port *port, struct ktermios *termios, atmel_uart_writel(port, ATMEL_US_CR, rts_state); } - /* set the baud rate */ + /* + * Set the baud rate: + * Fractional baudrate allows to setup output frequency more + * accurately. This feature is enabled only when using normal mode. + * baudrate = selected clock / (8 * (2 - OVER) * (CD + FP / 8)) + * Currently, OVER is always set to 0 so we get + * baudrate = selected clock (16 * (CD + FP / 8)) + */ + if (atmel_port->has_frac_baudrate && + (mode & ATMEL_US_USMODE) == ATMEL_US_USMODE_NORMAL) { + div = DIV_ROUND_CLOSEST(port->uartclk, baud); + cd = div / 16; + fp = DIV_ROUND_CLOSEST(div % 16, 2); + } else { + cd = uart_get_divisor(port, baud); + } + + if (cd > 65535) { /* BRGR is 16-bit, so switch to slower clock */ + cd /= 8; + mode |= ATMEL_US_USCLKS_MCK_DIV8; + } + quot = cd | fp << ATMEL_US_FP_OFFSET; + atmel_uart_writel(port, ATMEL_US_BRGR, quot); atmel_uart_writel(port, ATMEL_US_CR, ATMEL_US_RSTSTA | ATMEL_US_RSTRX); atmel_uart_writel(port, ATMEL_US_CR, ATMEL_US_TXEN | ATMEL_US_RXEN); |