linux-kernel - Re: [PATCH 2 1/9] serial: core: move RS485 configuration tasks from drivers into core

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Date:   Mon, 21 Feb 2022 19:39:56 +0100
From:   Greg KH <gregkh@...uxfoundation.org>
To:     Lino Sanfilippo <LinoSanfilippo@....de>
Cc:     jirislaby@...nel.org, u.kleine-koenig@...gutronix.de,
        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 2 1/9] serial: core: move RS485 configuration tasks from
 drivers into core

On Wed, Feb 16, 2022 at 01:17:55AM +0100, 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 | 18 ++++++++++++++++++
>  include/uapi/linux/serial.h      |  3 +++
>  2 files changed, 21 insertions(+)
> 
> diff --git a/drivers/tty/serial/serial_core.c b/drivers/tty/serial/serial_core.c
> index 846192a7b4bf..a4f7e847d414 100644
> --- a/drivers/tty/serial/serial_core.c
> +++ b/drivers/tty/serial/serial_core.c
> @@ -1282,8 +1282,26 @@ 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;
> +	}
> +
> +	rs485.delay_rts_before_send = min_t(unsigned int,
> +					    rs485.delay_rts_before_send,
> +					    SER_RS485_MAX_RTS_DELAY);
> +	rs485.delay_rts_after_send = min_t(unsigned int,
> +					   rs485.delay_rts_after_send,
> +					   SER_RS485_MAX_RTS_DELAY);
> +	/* Return clean padding area to userspace */
> +	memset(rs485.padding, 0, sizeof(rs485.padding));
> +
>  	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;
> diff --git a/include/uapi/linux/serial.h b/include/uapi/linux/serial.h
> index fa6b16e5fdd8..859045a53231 100644
> --- a/include/uapi/linux/serial.h
> +++ b/include/uapi/linux/serial.h
> @@ -128,6 +128,9 @@ struct serial_rs485 {
>  							   (if supported) */
>  	__u32	delay_rts_before_send;	/* Delay before send (milliseconds) */
>  	__u32	delay_rts_after_send;	/* Delay after send (milliseconds) */
> +#define SER_RS485_MAX_RTS_DELAY		100		/* Max time with active
> +							   RTS before/after
> +							   data sent (msecs) */

Why is this a userspace value now?  What can userspace do with this
number?  Once we add this, it's fixed for forever.

thanks,

greg k-h