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Commit 36131cdf authored by Alexey Starikovskiy's avatar Alexey Starikovskiy Committed by Greg Kroah-Hartman
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tty/serial: atmel: fix fractional baud rate computation 



The problem with previous code was it rounded values in wrong
place and produced wrong baud rate in some cases.

Signed-off-by: default avatarAlexey Starikovskiy <aystarik@gmail.com>
[nicolas.ferre@atmel.com: port to newer kernel and add commit log]
Signed-off-by: default avatarNicolas Ferre <nicolas.ferre@atmel.com>
Reviewed-by: default avatarBoris Brezillon <boris.brezillon@free-electrons.com>
Reviewed-by: default avatarUwe Kleine-König <u.kleine-koenig@pengutronix.de>
Signed-off-by: default avatarGreg Kroah-Hartman <gregkh@linuxfoundation.org>
parent e98d4137

drivers/tty/serial/atmel_serial.c

+6 −4
Original line number Diff line number Diff line
@@ -2170,13 +2170,15 @@ static void atmel_set_termios(struct uart_port *port, struct ktermios *termios, 
	 * 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))

	 * baudrate = selected clock / (16 * (CD + FP / 8))

	 * then

	 * 8 CD + FP = selected clock / (2 * baudrate)

	 */

	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);

		div = DIV_ROUND_CLOSEST(port->uartclk, baud * 2);

		cd = div >> 3;

		fp = div & ATMEL_US_FP_MASK;

	} else {

		cd = uart_get_divisor(port, baud);

	}

include/linux/atmel_serial.h

+1 −0
Original line number Diff line number Diff line
@@ -119,6 +119,7 @@ 
#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_FP_MASK	0x7



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

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