Patch "serial: mvebu-uart: correctly calculate minimal possible baudrate" has been added to the 5.13-stable tree

[Sasha Levin <sashal@xxxxxxxxxx>]

This is a note to let you know that I've just added the patch titled

    serial: mvebu-uart: correctly calculate minimal possible baudrate

to the 5.13-stable tree which can be found at:
    http://www.kernel.org/git/?p=linux/kernel/git/stable/stable-queue.git;a=summary

The filename of the patch is:
     serial-mvebu-uart-correctly-calculate-minimal-possib.patch
and it can be found in the queue-5.13 subdirectory.

If you, or anyone else, feels it should not be added to the stable tree,
please let <stable@xxxxxxxxxxxxxxx> know about it.



commit c0bdd5197de3cee462c3bd0a21327a323693bcd8
Author: Pali Rohár <pali@xxxxxxxxxx>
Date:   Fri Jun 25 00:49:02 2021 +0200

    serial: mvebu-uart: correctly calculate minimal possible baudrate
    
    [ Upstream commit deeaf963569a0d9d1b08babb771f61bb501a5704 ]
    
    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: Pali Rohár <pali@xxxxxxxxxx>
    Fixes: 68a0db1d7da2 ("serial: mvebu-uart: add function to change baudrate")
    Link: https://lore.kernel.org/r/20210624224909.6350-4-pali@xxxxxxxxxx
    Signed-off-by: Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx>
    Signed-off-by: Sasha Levin <sashal@xxxxxxxxxx>

diff --git a/drivers/tty/serial/mvebu-uart.c b/drivers/tty/serial/mvebu-uart.c
index 9638ae6aae79..1e26220c7852 100644
--- a/drivers/tty/serial/mvebu-uart.c
+++ b/drivers/tty/serial/mvebu-uart.c
@@ -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);