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

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Message-ID: <aa45fed9-7a40-7ac1-a000-18d2805d088f@kernel.org>
Date:   Mon, 14 Feb 2022 06:41:13 +0100
From:   Jiri Slaby <jirislaby@...nel.org>
To:     Lino Sanfilippo <LinoSanfilippo@....de>, gregkh@...uxfoundation.org
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
Subject: Re: [PATCH 1/9] serial: core: move RS485 configuration tasks from
 drivers into core

On 13. 02. 22, 23:27, Lino Sanfilippo wrote:
> Several drivers that support setting the RS485 configuration via userspace
> implement on 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 beheviour among all drivers.
> 
> Signed-off-by: Lino Sanfilippo <LinoSanfilippo@....de>
> ---
>   drivers/tty/serial/serial_core.c | 13 +++++++++++++
>   1 file changed, 13 insertions(+)
> 
> diff --git a/drivers/tty/serial/serial_core.c b/drivers/tty/serial/serial_core.c
> index 846192a7b4bf..3fab4070359c 100644
> --- a/drivers/tty/serial/serial_core.c
> +++ b/drivers/tty/serial/serial_core.c
> @@ -1282,8 +1282,21 @@ 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)) {
> +		rs485.flags |= SER_RS485_RTS_ON_SEND;
> +		rs485.flags &= ~SER_RS485_RTS_AFTER_SEND;
> +	}
> +	/* clamp the delays to [0, 100ms] */
> +	rs485.delay_rts_before_send = min(rs485.delay_rts_before_send, 100U);
> +	rs485.delay_rts_after_send = min(rs485.delay_rts_after_send, 100U);

Why is this magic 100? Can we have that number somehow documented? You 
should define a macro for that anyway.

> +	memset(rs485.padding, 0, sizeof(rs485.padding));

What is this memset good for?

>   	spin_lock_irqsave(&port->lock, flags);
>   	ret = port->rs485_config(port, &rs485);
> +	if (!ret)
> +		port->rs485 = rs485;
>   	spin_unlock_irqrestore(&port->lock, flags);
>   	if (ret)
>   		return ret;

thanks,
-- 
js
suse labs