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This can result in garbled output if the firmware or bootloader has already initialized the UART to a different speed. Introduce CONFIG_SERIAL_8250_PROBE_BAUD. When enabled, the driver will attempt to read the current baud rate from the hardware registers if no options are specified, rather than forcing the 9600 default. Signed-off-by: Sheng Yu --- drivers/tty/serial/8250/8250_core.c | 2 +- drivers/tty/serial/8250/8250_port.c | 6 +++++- drivers/tty/serial/8250/Kconfig | 12 ++++++++++++ 3 files changed, 18 insertions(+), 2 deletions(-) diff --git a/drivers/tty/serial/8250/8250_core.c b/drivers/tty/serial/8250/8250_core.c index 0e81f78c6063..c11b19921a1f 100644 --- a/drivers/tty/serial/8250/8250_core.c +++ b/drivers/tty/serial/8250/8250_core.c @@ -427,7 +427,7 @@ static int univ8250_console_setup(struct console *co, char *options) /* link port to console */ uart_port_set_cons(port, co); - retval = serial8250_console_setup(port, options, false); + retval = serial8250_console_setup(port, options, IS_ENABLED(CONFIG_SERIAL_8250_PROBE_BAUD)); if (retval != 0) uart_port_set_cons(port, NULL); return retval; diff --git a/drivers/tty/serial/8250/8250_port.c b/drivers/tty/serial/8250/8250_port.c index 719faf92aa8a..dbc0ef56f995 100644 --- a/drivers/tty/serial/8250/8250_port.c +++ b/drivers/tty/serial/8250/8250_port.c @@ -3399,8 +3399,12 @@ int serial8250_console_setup(struct uart_port *port, char *options, bool probe) if (options) uart_parse_options(options, &baud, &parity, &bits, &flow); - else if (probe) + else if (probe) { baud = probe_baud(port); + pr_info("console [%s%d] probed baud rate: %d\n", + port->cons->name, port->cons->index, baud); + + } ret = uart_set_options(port, port->cons, baud, parity, bits, flow); if (ret) diff --git a/drivers/tty/serial/8250/Kconfig b/drivers/tty/serial/8250/Kconfig index c488ff6f2865..bee6a82023d4 100644 --- a/drivers/tty/serial/8250/Kconfig +++ b/drivers/tty/serial/8250/Kconfig @@ -596,3 +596,15 @@ config SERIAL_OF_PLATFORM are probed through devicetree, including Open Firmware based PowerPC systems and embedded systems on architectures using the flattened device tree format. + +config SERIAL_8250_PROBE_BAUD + bool "Probe baud rate if console options are missing" + depends on SERIAL_8250 + help + If the "console=" command line parameter is missing options (e.g., + "console=ttyS0" instead of "console=ttyS0,115200n8"), this option + allows the kernel to probe the baud rate from hardware instead of + defaulting to 9600. + + If a baud rate is explicitly provided in the options, that value + is always respected. -- 2.51.0