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Commit 5bf5635a authored by Ludovic Desroches's avatar Ludovic Desroches Committed by Greg Kroah-Hartman
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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: default avatarLudovic Desroches <ludovic.desroches@atmel.com>
Acked-by: default avatarNicolas Ferre <nicolas.ferre@atmel.com>
Signed-off-by: default avatarGreg Kroah-Hartman <gregkh@linuxfoundation.org>
parent 2426fbc7

drivers/tty/serial/atmel_serial.c

+33 −8
Original line number Diff line number Diff line
@@ -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);

include/linux/atmel_serial.h

+1 −0
Original line number Diff line number Diff line
@@ -118,6 +118,7 @@ 


#define ATMEL_US_BRGR		0x20	/* Baud Rate Generator Register */

#define	ATMEL_US_CD		GENMASK(15, 0)	/* Clock Divider */

#define ATMEL_US_FP_OFFSET	16	/* Fractional Part */



#define ATMEL_US_RTOR		0x24	/* Receiver Time-out Register for USART */

#define ATMEL_UA_RTOR		0x28	/* Receiver Time-out Register for UART */