linux-kernel - Re: [PATCH v3] tty: serial: Add RS422 flag to struct serial

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Date:   Thu, 9 Nov 2023 15:35:50 +0200 (EET)
From:   Ilpo Järvinen <ilpo.jarvinen@...ux.intel.com>
To:     Crescent CY Hsieh <crescentcy.hsieh@...a.com>
cc:     Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        Jiri Slaby <jirislaby@...nel.org>,
        LKML <linux-kernel@...r.kernel.org>,
        linux-serial <linux-serial@...r.kernel.org>
Subject: Re: [PATCH v3] tty: serial: Add RS422 flag to struct serial_rs485

On Wed, 8 Nov 2023, 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.
> 
> There are only two things need to be noticed:
> 
> - While enabling RS422, other RS485 flags should not be set.
> - RS422 doesn't need to deal with termination, so while disabling RS485
>   or enabling RS422, uart_set_rs485_termination() shall return.
> 
> Signed-off-by: Crescent CY Hsieh <crescentcy.hsieh@...a.com>
> 
> ---
> 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.
> 
> 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/
> 
> ---

> --- a/include/uapi/linux/serial.h
> +++ b/include/uapi/linux/serial.h
> @@ -137,17 +137,19 @@ struct serial_icounter_struct {
>   * * %SER_RS485_ADDRB		- Enable RS485 addressing mode.
>   * * %SER_RS485_ADDR_RECV - Receive address filter (enables @addr_recv). Requires %SER_RS485_ADDRB.
>   * * %SER_RS485_ADDR_DEST - Destination address (enables @addr_dest). Requires %SER_RS485_ADDRB.
> + * * %SER_RS485_MODE_RS422	- Enable RS422. Requires %SER_RS485_ENABLED.
>   */
>  struct serial_rs485 {
>  	__u32	flags;
> -#define SER_RS485_ENABLED		(1 << 0)
> -#define SER_RS485_RTS_ON_SEND		(1 << 1)
> -#define SER_RS485_RTS_AFTER_SEND	(1 << 2)
> -#define SER_RS485_RX_DURING_TX		(1 << 4)
> -#define SER_RS485_TERMINATE_BUS		(1 << 5)
> -#define SER_RS485_ADDRB			(1 << 6)
> -#define SER_RS485_ADDR_RECV		(1 << 7)
> -#define SER_RS485_ADDR_DEST		(1 << 8)
> +#define SER_RS485_ENABLED		BIT(0)
> +#define SER_RS485_RTS_ON_SEND		BIT(1)
> +#define SER_RS485_RTS_AFTER_SEND	BIT(2)
> +#define SER_RS485_RX_DURING_TX		BIT(3)
> +#define SER_RS485_TERMINATE_BUS		BIT(4)
> +#define SER_RS485_ADDRB			BIT(5)
> +#define SER_RS485_ADDR_RECV		BIT(6)
> +#define SER_RS485_ADDR_DEST		BIT(7)
> +#define SER_RS485_MODE_RS422		BIT(8)

Is BIT() allowed in uapi headers these days?

-- 
 i.