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Date: Mon, 13 Nov 2023 14:13:22 +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 v4] tty: serial: Add RS422 flag to struct serial_rs485
Hi,
On 13.11.23 10:41, 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.
Commit messages should use the imperative form.
>
> Signed-off-by: Crescent CY Hsieh <crescentcy.hsieh@...a.com>
>
> ---
> 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.
>
> 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 | 11 ++++++++++-
> include/uapi/linux/serial.h | 19 +++++++++++--------
> 2 files changed, 21 insertions(+), 9 deletions(-)
>
> diff --git a/drivers/tty/serial/serial_core.c b/drivers/tty/serial/serial_core.c
> index 831d03361..777f091a4 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)> + return;
> + }
> +
> /* Pick sane settings if the user hasn't */
> if ((supported_flags & (SER_RS485_RTS_ON_SEND|SER_RS485_RTS_AFTER_SEND)) &&
> !(rs485->flags & SER_RS485_RTS_ON_SEND) ==
> @@ -1400,7 +1407,9 @@ static void uart_sanitize_serial_rs485(struct uart_port *port, struct serial_rs4
> static void uart_set_rs485_termination(struct uart_port *port,
> const struct serial_rs485 *rs485)
> {
> - if (!(rs485->flags & SER_RS485_ENABLED))
> + /* Return while disabling RS485 or enabling RS422 */
> + if (!(rs485->flags & SER_RS485_ENABLED) ||
> + (rs485->flags & SER_RS485_ENABLED && rs485->flags & SER_RS485_MODE_RS422))
Is this check needed at all? If no termination GPIO is specified, gpiod_set_value_cansleep()
does nothing. If a termination GPIO is specified it will be deasserted in case of RS422
(since for the RS422 case the SER_RS485_TERMINATE_BUS flag is deleted in
uart_sanitize_serial_rs485()). This seems like a good behaviour to me, so IMO the above check
is not needed.
>
> gpiod_set_value_cansleep(port->rs485_term_gpio,
> diff --git a/include/uapi/linux/serial.h b/include/uapi/linux/serial.h
> index 53bc1af67..9086367db 100644
> --- a/include/uapi/linux/serial.h
> +++ b/include/uapi/linux/serial.h
> @@ -11,6 +11,7 @@
> #ifndef _UAPI_LINUX_SERIAL_H
> #define _UAPI_LINUX_SERIAL_H
>
> +#include <linux/const.h>
> #include <linux/types.h>
>
> #include <linux/tty_flags.h>
> @@ -137,17 +138,19 @@ 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.
All of the above flags are only effective if RS485_ENABLED is set, so no need
to mention this explicitly for the MODE_RS422 flag.
> */
> 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 _BITUL(0)
> +#define SER_RS485_RTS_ON_SEND _BITUL(1)
> +#define SER_RS485_RTS_AFTER_SEND _BITUL(2)
> +#define SER_RS485_RX_DURING_TX _BITUL(3)
> +#define SER_RS485_TERMINATE_BUS _BITUL(4)
> +#define SER_RS485_ADDRB _BITUL(5)
> +#define SER_RS485_ADDR_RECV _BITUL(6)
> +#define SER_RS485_ADDR_DEST _BITUL(7)
> +#define SER_RS485_MODE_RS422 _BITUL(8)
>
> __u32 delay_rts_before_send;
> __u32 delay_rts_after_send;
Regards,
Lino
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