linux-kernel - Re: [PATCH v5] tty: serial: Add RS422 flag to struct serial

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Message-ID: <aa1f0e1e-1587-592c-7e86-e8f168b71c21@gmx.de>
Date:   Fri, 24 Nov 2023 22:06:19 +0100
From:   Lino Sanfilippo <LinoSanfilippo@....de>
To:     Crescent CY Hsieh <crescentcy.hsieh@...a.com>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        Jiri Slaby <jirislaby@...nel.org>
Cc:     linux-kernel@...r.kernel.org, linux-serial@...r.kernel.org
Subject: Re: [PATCH v5] tty: serial: Add RS422 flag to struct serial_rs485

On 21.11.23 at 10:51, Crescent CY Hsieh wrote:
> Add "SER_RS485_MODE_RS422" flag to struct serial_rs485, so that serial
> port can switch interface into RS422 if supported by using ioctl command
> "TIOCSRS485".
>
> By treating RS422 as a mode of RS485, which means while enabling RS422
> there are two flags need to be set (SER_RS485_ENABLED and
> SER_RS485_MODE_RS422), it would make things much easier. For example
> some places that checks for "SER_RS485_ENABLED" won't need to be rewritten.
>
> Signed-off-by: Crescent CY Hsieh <crescentcy.hsieh@...a.com>
>
> ---
> Changes from v4 to v5:
> - Revise commit message.
> - Delete RS422 checks within uart_set_rs485_termination().
>
> Changes from v3 to v4:
> - Include 'linux/const.h' header in '/include/uapi/linux/serial.h'
> - Replace BIT() with _BITUL() which defined in
>   '/include/uapi/linux/const.h'
>
> Changes from v2 to v3:
> - Remove "SER_RS422_ENABLED" flag from legacy flags.
> - Revise "SER_RS422_ENABLED" into "SER_RS485_MODE_RS422".
> - Remove the code which checks the conflicts between SER_RS485_ENABLED
>   and SER_RS422_ENABLED.
> - Add return check in uart_set_rs485_termination().
>
> Changes from v1 to v2:
> - Revise the logic that checks whether RS422/RS485 are enabled
>   simultaneously.
>
> v4: https://lore.kernel.org/all/20231113094136.52003-1-crescentcy.hsieh@moxa.com/
> v3: https://lore.kernel.org/all/20231108060719.11775-1-crescentcy.hsieh@moxa.com/
> v2: https://lore.kernel.org/all/20231101064404.45711-1-crescentcy.hsieh@moxa.com/
> v1: https://lore.kernel.org/all/20231030053632.5109-1-crescentcy.hsieh@moxa.com/
>
> ---
>  drivers/tty/serial/serial_core.c |  7 +++++++
>  include/uapi/linux/serial.h      | 19 +++++++++++--------
>  2 files changed, 18 insertions(+), 8 deletions(-)
>
> diff --git a/drivers/tty/serial/serial_core.c b/drivers/tty/serial/serial_core.c
> index 831d03361..db1ebed7f 100644
> --- a/drivers/tty/serial/serial_core.c
> +++ b/drivers/tty/serial/serial_core.c
> @@ -1376,6 +1376,13 @@ static void uart_sanitize_serial_rs485(struct uart_port *port, struct serial_rs4
>  		return;
>  	}
>
> +	/* Clear other RS485 flags and return if enabling RS422 */
> +	if (rs485->flags & SER_RS485_MODE_RS422) {
> +		memset(rs485, 0, sizeof(*rs485));
> +		rs485->flags |= (SER_RS485_ENABLED | SER_RS485_MODE_RS422);

Does not RS422 also require termination resistors? So what about SER_RS485_TERMINATE_BUS?

Regards,
Lino