linux-kernel - Re: [PATCH] tty: serial: qcom_geni_serial: 115.2 is a better console default than 9600

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Date:   Fri, 11 Sep 2020 08:55:42 -0700
From:   Nathan Chancellor <natechancellor@...il.com>
To:     Douglas Anderson <dianders@...omium.org>
Cc:     Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        Nick Desaulniers <ndesaulniers@...gle.com>,
        robdclark@...omium.org, Akash Asthana <akashast@...eaurora.org>,
        jwerner@...omium.org, Andy Gross <agross@...nel.org>,
        Bjorn Andersson <bjorn.andersson@...aro.org>,
        Jiri Slaby <jirislaby@...nel.org>,
        linux-arm-msm@...r.kernel.org, linux-kernel@...r.kernel.org,
        linux-serial@...r.kernel.org
Subject: Re: [PATCH] tty: serial: qcom_geni_serial: 115.2 is a better console
 default than 9600

On Fri, Sep 11, 2020 at 08:00:57AM -0700, Douglas Anderson wrote:
> Commit c5cbc78acf69 ("tty: serial: qcom_geni_serial: Initialize baud
> in qcom_geni_console_setup") fixed a bug by initting a variable that
> was used in some cases without initialization.  However, the "default"
> baud rate picked by that CL was probably not the best choice.  The
> chances that anyone out there is trying to run a system with kernel
> messages piped out over a 9600 baud serial port is just about nil.
> Console messages are printed in a blocking manner.  At 9600 baud we
> print about 1 character per millisecond which means that printing a
> 40-byte message to the console will take ~40 ms.  While it would
> probably work, it's going to make boot _very_ slow and probably cause
> the occasional timeout here and there in drivers (heck, even at 115200
> console delays can wreck havoc).
> 
> This has already bit at least two people that I'm aware of that tried
> to enable serial console by just adding "console=ttyMSM0" (instead of
> "console=ttyMSM0,115200n8") to the command line, so it seems like it'd
> be nice to fix.
> 
> Let's switch the default to 115200.
> 
> Signed-off-by: Douglas Anderson <dianders@...omium.org>

Reviewed-by: Nathan Chancellor <natechancellor@...il.com>

> ---
> 
>  drivers/tty/serial/qcom_geni_serial.c | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
> 
> diff --git a/drivers/tty/serial/qcom_geni_serial.c b/drivers/tty/serial/qcom_geni_serial.c
> index f0b1b47c3abc..e390ffc8bbbd 100644
> --- a/drivers/tty/serial/qcom_geni_serial.c
> +++ b/drivers/tty/serial/qcom_geni_serial.c
> @@ -1107,7 +1107,7 @@ static int qcom_geni_console_setup(struct console *co, char *options)
>  {
>  	struct uart_port *uport;
>  	struct qcom_geni_serial_port *port;
> -	int baud = 9600;
> +	int baud = 115200;
>  	int bits = 8;
>  	int parity = 'n';
>  	int flow = 'n';
> -- 
> 2.28.0.618.gf4bc123cb7-goog
>