linux-kernel - Re: [PATCH] serial: 8250: Fix restoring termios speed after suspend

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Date:   Mon, 26 Sep 2022 09:16:43 +0200
From:   Jiri Slaby <jirislaby@...nel.org>
To:     Pali Rohár <pali@...nel.org>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>
Cc:     linux-serial@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH] serial: 8250: Fix restoring termios speed after suspend

On 24. 09. 22, 12:43, Pali Rohár wrote:
> Since commit edc6afc54968 ("tty: switch to ktermios and new framework")
> termios speed is no longer stored only in c_cflag member but also in new
> additional c_ispeed and c_ospeed members. If BOTHER flag is set in c_cflag
> then termios speed is stored only in these new members.
> 
> Since commit 027b57170bf8 ("serial: core: Fix initializing and restoring
> termios speed") termios speed is available also in struct console.
> 
> So properly restore also c_ispeed and c_ospeed members after suspend to fix
> restoring termios speed which is not represented by Bnnn constant.
> 
> Fixes: 4516d50aabed ("serial: 8250: Use canary to restart console after suspend")
> Signed-off-by: Pali Rohár <pali@...nel.org>
> ---
>   drivers/tty/serial/8250/8250_port.c | 7 ++++++-
>   1 file changed, 6 insertions(+), 1 deletion(-)
> 
> diff --git a/drivers/tty/serial/8250/8250_port.c b/drivers/tty/serial/8250/8250_port.c
> index 39b35a61958c..441f317c55af 100644
> --- a/drivers/tty/serial/8250/8250_port.c
> +++ b/drivers/tty/serial/8250/8250_port.c
> @@ -3314,8 +3314,13 @@ static void serial8250_console_restore(struct uart_8250_port *up)
>   	unsigned int baud, quot, frac = 0;
>   
>   	termios.c_cflag = port->cons->cflag;
> -	if (port->state->port.tty && termios.c_cflag == 0)
> +	termios.c_ispeed = port->cons->ispeed;
> +	termios.c_ospeed = port->cons->ospeed;
> +	if (port->state->port.tty && termios.c_cflag == 0) {

I don't currently know how safe it is to assume port->state->port.tty 
cannot change between the test above and the dereferences below.

In anyway, you should cache it as it is used 4 times now. It would make 
the code definitely more readable.

>   		termios.c_cflag = port->state->port.tty->termios.c_cflag;
> +		termios.c_ispeed = port->state->port.tty->termios.c_ispeed;
> +		termios.c_ospeed = port->state->port.tty->termios.c_ospeed;
> +	}
>   
>   	baud = serial8250_get_baud_rate(port, &termios, NULL);
>   	quot = serial8250_get_divisor(port, baud, &frac);

-- 
js
suse labs