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

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Date:   Mon, 14 Feb 2022 08:06:22 +0100
From:   Uwe Kleine-König <u.kleine-koenig@...gutronix.de>
To:     Lino Sanfilippo <LinoSanfilippo@....de>
Cc:     gregkh@...uxfoundation.org, jirislaby@...nel.org,
        linux-arm-kernel@...ts.infradead.org,
        alexandre.belloni@...tlin.com, mcoquelin.stm32@...il.com,
        richard.genoud@...il.com, festevam@...il.com,
        s.hauer@...gutronix.de, linux@...linux.org.uk,
        nicolas.ferre@...rochip.com, alexandre.torgue@...s.st.com,
        ludovic.desroches@...rochip.com, lukas@...ner.de,
        linux-imx@....com, kernel@...gutronix.de,
        linux-serial@...r.kernel.org, shawnguo@...nel.org,
        linux-stm32@...md-mailman.stormreply.com,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH 1/9] serial: core: move RS485 configuration tasks from
 drivers into core

On Sun, Feb 13, 2022 at 11:27:29PM +0100, Lino Sanfilippo wrote:
> Several drivers that support setting the RS485 configuration via userspace
> implement on or more of the following tasks:

s/on/one/

> 
> - 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.

s/beheviour/behaviour/

> 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);
> +	memset(rs485.padding, 0, sizeof(rs485.padding));
> +
>  	spin_lock_irqsave(&port->lock, flags);
>  	ret = port->rs485_config(port, &rs485);
> +	if (!ret)
> +		port->rs485 = rs485;

I was only Cc:d for the imx patch (patch #7) and tried to verify the
claim there that "the serial core already assigns the passed
configuration to the uart port". That failed when I looked at my kernel
tree.

So it would be great, if you sent dependencies (or at least a cover
letter) to all recipients of a given patch to ease review. Also I want
to suggest to mention uart_set_rs485_config() in the commit log of the
imx patch (and probably the others) to simplify verifying the claim
there.

Thanks
Uwe

-- 
Pengutronix e.K.                           | Uwe Kleine-König            |
Industrial Linux Solutions                 | https://www.pengutronix.de/ |

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