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

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Message-Id: <20231108060719.11775-1-crescentcy.hsieh@moxa.com>
Date:   Wed,  8 Nov 2023 14:07:19 +0800
From:   Crescent CY Hsieh <crescentcy.hsieh@...a.com>
To:     Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        Jiri Slaby <jirislaby@...nel.org>
Cc:     linux-kernel@...r.kernel.org, linux-serial@...r.kernel.org,
        Crescent CY Hsieh <crescentcy.hsieh@...a.com>
Subject: [PATCH v3] tty: serial: Add RS422 flag to struct serial_rs485

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/

---
 drivers/tty/serial/serial_core.c | 11 ++++++++++-
 include/uapi/linux/serial.h      | 18 ++++++++++--------
 2 files changed, 20 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))
 		return;
 
 	gpiod_set_value_cansleep(port->rs485_term_gpio,
diff --git a/include/uapi/linux/serial.h b/include/uapi/linux/serial.h
index 53bc1af67..c9c4d3b00 100644
--- 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)
 
 	__u32	delay_rts_before_send;
 	__u32	delay_rts_after_send;
-- 
2.34.1