Commit deeaf963 authored by Pali Rohár's avatar Pali Rohár Committed by Greg Kroah-Hartman
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serial: mvebu-uart: correctly calculate minimal possible baudrate 



For default (x16) scheme which is currently used by mvebu-uart.c driver,
maximal divisor of UART base clock is 1023*16. Therefore there is limit for
minimal supported baudrate. This change calculate it correctly and prevents
setting invalid divisor 0 into hardware registers.

Signed-off-by: default avatarPali Rohár <pali@kernel.org>
Fixes: 68a0db1d ("serial: mvebu-uart: add function to change baudrate")
Link: https://lore.kernel.org/r/20210624224909.6350-4-pali@kernel.org


Signed-off-by: default avatarGreg Kroah-Hartman <gregkh@linuxfoundation.org>
parent ecd6b010

drivers/tty/serial/mvebu-uart.c

+8 −3
Original line number Diff line number Diff line
@@ -481,7 +481,7 @@ static void mvebu_uart_set_termios(struct uart_port *port, 
				   struct ktermios *old)

{

	unsigned long flags;

	unsigned int baud;

	unsigned int baud, min_baud, max_baud;



	spin_lock_irqsave(&port->lock, flags);
@@ -500,16 +500,21 @@ static void mvebu_uart_set_termios(struct uart_port *port, 
		port->ignore_status_mask |= STAT_RX_RDY(port) | STAT_BRK_ERR;



	/*

	 * Maximal divisor is 1023 * 16 when using default (x16) scheme.

	 * Maximum achievable frequency with simple baudrate divisor is 230400.

	 * Since the error per bit frame would be of more than 15%, achieving

	 * higher frequencies would require to implement the fractional divisor

	 * feature.

	 */

	baud = uart_get_baud_rate(port, termios, old, 0, 230400);

	min_baud = DIV_ROUND_UP(port->uartclk, 1023 * 16);

	max_baud = 230400;



	baud = uart_get_baud_rate(port, termios, old, min_baud, max_baud);

	if (mvebu_uart_baud_rate_set(port, baud)) {

		/* No clock available, baudrate cannot be changed */

		if (old)

			baud = uart_get_baud_rate(port, old, NULL, 0, 230400);

			baud = uart_get_baud_rate(port, old, NULL,

						  min_baud, max_baud);

	} else {

		tty_termios_encode_baud_rate(termios, baud, baud);

		uart_update_timeout(port, termios->c_cflag, baud);