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

serial: 8250_early: Only set divisor if valid clk & baud

to the 4.14-stable tree which can be found at: http://www.kernel.org/git/?p=linux/kernel/git/stable/stable-queue.git%3Ba=su...

The filename of the patch is: serial-8250_early-only-set-divisor-if-valid-clk-baud.patch and it can be found in the queue-4.14 subdirectory.

If you, or anyone else, feels it should not be added to the stable tree, please let stable@vger.kernel.org know about it.

From 0ff3ab701963a845d52337ded7eebf2d1a14fe00 Mon Sep 17 00:00:00 2001

From: Matt Redfearn matt.redfearn@mips.com Date: Wed, 22 Nov 2017 09:57:28 +0000 Subject: serial: 8250_early: Only set divisor if valid clk & baud

From: Matt Redfearn matt.redfearn@mips.com

commit 0ff3ab701963a845d52337ded7eebf2d1a14fe00 upstream.

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") Signed-off-by: Matt Redfearn matt.redfearn@mips.com Signed-off-by: Greg Kroah-Hartman gregkh@linuxfoundation.org

--- drivers/tty/serial/8250/8250_early.c | 14 ++++++++------ 1 file changed, 8 insertions(+), 6 deletions(-)

--- 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 earl 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,

Patches currently in stable-queue which might be from matt.redfearn@mips.com are

queue-4.14/mips-add-custom-serial.h-with-base_baud-override-for-generic-kernel.patch queue-4.14/serial-8250_early-only-set-divisor-if-valid-clk-baud.patch