linux-kernel - Re: [PATCH v3 1/9] serial: core: move RS485 configuration tasks from drivers into core

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Date:   Tue, 22 Feb 2022 07:51:39 +0100
From:   Jiri Slaby <jirislaby@...nel.org>
To:     Lino Sanfilippo <LinoSanfilippo@....de>,
        gregkh@...uxfoundation.org, u.kleine-koenig@...gutronix.de
Cc:     linux@...linux.org.uk, richard.genoud@...il.com,
        nicolas.ferre@...rochip.com, alexandre.belloni@...tlin.com,
        ludovic.desroches@...rochip.com, shawnguo@...nel.org,
        s.hauer@...gutronix.de, kernel@...gutronix.de, festevam@...il.com,
        linux-imx@....com, mcoquelin.stm32@...il.com,
        alexandre.torgue@...s.st.com, linux-serial@...r.kernel.org,
        linux-kernel@...r.kernel.org, linux-arm-kernel@...ts.infradead.org,
        linux-stm32@...md-mailman.stormreply.com, lukas@...ner.de,
        p.rosenberger@...bus.com
Subject: Re: [PATCH v3 1/9] serial: core: move RS485 configuration tasks from
 drivers into core

On 22. 02. 22, 2:14, Lino Sanfilippo wrote:
> Several drivers that support setting the RS485 configuration via userspace
> implement one or more of the following tasks:
> 
> - in case of an invalid RTS configuration (both RTS after send and RTS on
>    send set or both unset) fall back to enable RTS on send and disable RTS
>    after send
> 
> - nullify the padding field of the returned serial_rs485 struct
> 
> - copy the configuration into the uart port struct
> 
> - limit RTS delays to 100 ms
> 
> Move these tasks into the serial core to make them generic and to provide
> a consistent behaviour among all drivers.
> 
> Signed-off-by: Lino Sanfilippo <LinoSanfilippo@....de>
> ---
>   drivers/tty/serial/serial_core.c | 29 +++++++++++++++++++++++++++++
>   1 file changed, 29 insertions(+)
> 
> diff --git a/drivers/tty/serial/serial_core.c b/drivers/tty/serial/serial_core.c
> index 846192a7b4bf..2b3afe038c1c 100644
> --- a/drivers/tty/serial/serial_core.c
> +++ b/drivers/tty/serial/serial_core.c
> @@ -42,6 +42,11 @@ static struct lock_class_key port_lock_key;
>   
>   #define HIGH_BITS_OFFSET	((sizeof(long)-sizeof(int))*8)
>   
> +/*
> + * Max time with active RTS before/after data is sent.
> + */
> +#define RS485_MAX_RTS_DELAY	100 /* msecs */
> +
>   static void uart_change_speed(struct tty_struct *tty, struct uart_state *state,
>   					struct ktermios *old_termios);
>   static void uart_wait_until_sent(struct tty_struct *tty, int timeout);
> @@ -1282,8 +1287,32 @@ static int uart_set_rs485_config(struct uart_port *port,
>   	if (copy_from_user(&rs485, rs485_user, sizeof(*rs485_user)))
>   		return -EFAULT;
>   
> +	/* pick sane settings if the user hasn't */
> +	if (!(rs485.flags & SER_RS485_RTS_ON_SEND) ==
> +	    !(rs485.flags & SER_RS485_RTS_AFTER_SEND)) {
> +		pr_warn("invalid RTS setting, using RTS_ON_SEND instead\n");

Can't we have a device prefix here, so that everyone knows what device 
is affected? Without that, it's not that useful. At least port->name & 
port->line could be printed. The uart core uses dev_* prints, but prints 
also line as uport->dev can be NULL sometimes.

Hm, we could introduce uart_print family (to print something like what 
is in uart_report_port).

thanks,
-- 
js
suse labs