Re: [PATCH] serial: 8250_early: Setup divider when uartclk is passed

From: Matt Redfearn
Date: Mon Apr 23 2018 - 09:21:52 EST

Hi Michal

On 23/04/18 10:18, Michal Simek wrote:
device->baud is always non zero value because it is checked already in
early_serial8250_setup() before init_port is called.

True, currently init_port is only called from the one location and so the test is a little redundant, though I don't see the harm in testing both inputs to the divisor calculation immediately before use such that any future call path avoids setting a bad divisor.

Fixes: 0ff3ab701963 ("serial: 8250_early: Only set divisor if valid clk & baud")
Cc: stable <stable@xxxxxxxxxxxxxxx>

Even if the test is dropped going forward, I wouldn't consider it's presence a "bug" such that a fix needs to be backported.


Signed-off-by: Michal Simek <michal.simek@xxxxxxxxxx>

drivers/tty/serial/8250/8250_early.c | 2 +-
1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/drivers/tty/serial/8250/8250_early.c b/drivers/tty/serial/8250/8250_early.c
index ae6a256524d8..5cd8c36c8fcc 100644
--- a/drivers/tty/serial/8250/8250_early.c
+++ b/drivers/tty/serial/8250/8250_early.c
@@ -122,7 +122,7 @@ 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 */
- if (port->uartclk && device->baud) {
+ if (port->uartclk) {
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);