serial: atmel: fix incorrect baudrate setup

commit 5bfdd3c654bd879bff50c2e85e42f85ae698b42f upstream.

Commit ef5def31c40e ("serial: core: remove baud_rates when serial console
setup") changed uart_set_options to select the correct baudrate
configuration based on the absolute error between requested baudrate and
available standard baudrate settings.
Prior to that commit the baudrate was selected based on which predefined
standard baudrate did not exceed the requested baudrate.
This change of selection logic was never reflected in the atmel serial
driver. Thus the comment left in the atmel serial driver is no longer
accurate.
Additionally the manual rounding up described in that comment and applied
via (quot - 1) requests an incorrect baudrate. Since uart_set_options uses
tty_termios_encode_baud_rate to determine the appropriate baudrate flags
this can cause baudrate selection to fail entirely because
tty_termios_encode_baud_rate will only select a baudrate if relative error
between requested and selected baudrate does not exceed +/-2%.
Fix that by requesting actual, exact baudrate used by the serial.

Fixes: ef5def31c40e ("serial: core: remove baud_rates when serial console setup")
Cc: stable <stable@kernel.org>
Signed-off-by: Tobias Schramm <t.schramm@manjaro.org>
Acked-by: Richard Genoud <richard.genoud@gmail.com>
Link: https://lore.kernel.org/r/20230109072940.202936-1-t.schramm@manjaro.org
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

diff --git a/drivers/tty/serial/atmel_serial.c b/drivers/tty/serial/atmel_serial.c
index 3bd93558b4435f2db7d36d8eac1c4c98c40f4287..6c0628c58efd917a7d3072567ce5ec465541cff4 100644 (file)
--- a/drivers/tty/serial/atmel_serial.c
+++ b/drivers/tty/serial/atmel_serial.c
@@ -2642,13 +2642,7 @@ static void __init atmel_console_get_options(struct uart_port *port, int *baud,
        else if (mr == ATMEL_US_PAR_ODD)
                *parity = 'o';
 
-       /*
-        * The serial core only rounds down when matching this to a
-        * supported baud rate. Make sure we don't end up slightly
-        * lower than one of those, as it would make us fall through
-        * to a much lower baud rate than we really want.
-        */
-       *baud = port->uartclk / (16 * (quot - 1));
+       *baud = port->uartclk / (16 * quot);
 }
 
 static int __init atmel_console_setup(struct console *co, char *options)