If either uartclk or baud are 0, avoid calculating and setting a divisor based on them since the output will almost certainly be garbage.
This also allows platforms such as the MIPS generic kernel, which has no way to know a valid BASE_BASE for the board it is actually booted on at compile time, to set BASE_BAUD to 0 and avoid early_8250 setting a bad divisor.
This fixes a regression caused by commit 31cb9a8575ca ("earlycon: initialise baud field of earlycon device structure"), which changed the behavior of of_setup_earlycon such that it sets a baud rate in the earlycon structure where previously it was left as 0. All boards supported by the MIPS generic kernel started outputting garbage from the boot console due to an incorrect divisor being set.
Fixes: 31cb9a8575ca ("earlycon: initialise baud field of earlycon device structure") Cc: stable stable@vger.kernel.org # 4.14 Signed-off-by: Matt Redfearn matt.redfearn@mips.com ---
drivers/tty/serial/8250/8250_early.c | 14 ++++++++------ 1 file changed, 8 insertions(+), 6 deletions(-)
diff --git a/drivers/tty/serial/8250/8250_early.c b/drivers/tty/serial/8250/8250_early.c index af72ec32e404..f135c1846477 100644 --- a/drivers/tty/serial/8250/8250_early.c +++ b/drivers/tty/serial/8250/8250_early.c @@ -125,12 +125,14 @@ static void __init init_port(struct earlycon_device *device) serial8250_early_out(port, UART_FCR, 0); /* no fifo */ serial8250_early_out(port, UART_MCR, 0x3); /* DTR + RTS */
- divisor = DIV_ROUND_CLOSEST(port->uartclk, 16 * device->baud); - c = serial8250_early_in(port, UART_LCR); - serial8250_early_out(port, UART_LCR, c | UART_LCR_DLAB); - serial8250_early_out(port, UART_DLL, divisor & 0xff); - serial8250_early_out(port, UART_DLM, (divisor >> 8) & 0xff); - serial8250_early_out(port, UART_LCR, c & ~UART_LCR_DLAB); + if (port->uartclk && device->baud) { + divisor = DIV_ROUND_CLOSEST(port->uartclk, 16 * device->baud); + c = serial8250_early_in(port, UART_LCR); + serial8250_early_out(port, UART_LCR, c | UART_LCR_DLAB); + serial8250_early_out(port, UART_DLL, divisor & 0xff); + serial8250_early_out(port, UART_DLM, (divisor >> 8) & 0xff); + serial8250_early_out(port, UART_LCR, c & ~UART_LCR_DLAB); + } }
int __init early_serial8250_setup(struct earlycon_device *device,