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From:   Crescent CY Hsieh <crescentcy.hsieh@moxa.com>
To:     gregkh@linuxfoundation.org, jirislaby@kernel.org
Cc:     linux-kernel@vger.kernel.org, linux-serial@vger.kernel.org,
        Crescent CY Hsieh <crescentcy.hsieh@moxa.com>
Subject: [PATCH 4/4] tty: serial: 8250: Add support for MOXA PCIe boards to switch interface between RS422/RS485
Date:   Mon,  2 Oct 2023 09:57:02 +0800
Message-Id: <20231002015702.30509-5-crescentcy.hsieh@moxa.com>
In-Reply-To: <20231002015702.30509-1-crescentcy.hsieh@moxa.com>
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MOXA PCIe boards have 4 serial interfaces and don't require additional
stuff to switch between interfaces:

- RS232
- RS422
- RS485_2W (half-duplex)
- RS485_4W (full-duplex)

By using ioctl command "TIOCRS485", it can switch between default
interface and RS485 if supported.

That means, for RS422/RS485 board, it can switch between RS422 and
RS485 by setting the flags within struct serial_rs485.

However, for the RS232/RS422/RS485 board, it can only switch between
RS232 and RS485, there's no flag for switching interface into RS422.

This patch adds a flag call "SER_RS422_ENALBED" in serial.h and modifies
serial_core.c to make it possible to switch interface between RS232,
RS422 and RS485.

Signed-off-by: Crescent CY Hsieh <crescentcy.hsieh@moxa.com>
---
 drivers/tty/serial/8250/8250_pci.c | 41 ++++++++++++++++++++++++++++++
 drivers/tty/serial/serial_core.c   | 20 ++++++++++++---
 include/uapi/linux/serial.h        |  4 +++
 3 files changed, 61 insertions(+), 4 deletions(-)

diff --git a/drivers/tty/serial/8250/8250_pci.c b/drivers/tty/serial/8250/8250_pci.c
index 31bfe5381000..86dce37f08c0 100644
--- a/drivers/tty/serial/8250/8250_pci.c
+++ b/drivers/tty/serial/8250/8250_pci.c
@@ -1898,6 +1898,10 @@ pci_sunix_setup(struct serial_private *priv,
 
 #define MOXA_GPIO_SET_ALL_OUTPUT	0x0F
 
+static const struct serial_rs485 pci_moxa_rs485_supported = {
+	.flags = SER_RS485_ENABLED | SER_RS485_RX_DURING_TX | SER_RS422_ENABLED,
+};
+
 static int pci_moxa_set_interface(struct pci_dev *dev,
 				  unsigned int port_idx,
 				  unsigned char mode)
@@ -1921,6 +1925,30 @@ static int pci_moxa_set_interface(struct pci_dev *dev,
 	return 0;
 }
 
+static int pci_moxa_rs485_config(struct uart_port *port,
+				 struct ktermios *termios,
+				 struct serial_rs485 *rs485)
+{
+	struct pci_dev *dev = to_pci_dev(port->dev);
+	unsigned short device = dev->device;
+	unsigned char mode = MOXA_RS232;
+
+	if (rs485->flags & SER_RS485_ENABLED) {
+		if (rs485->flags & SER_RS485_RX_DURING_TX)
+			mode = MOXA_RS485_4W;
+		else
+			mode = MOXA_RS485_2W;
+	} else if (rs485->flags & SER_RS422_ENABLED) {
+		mode = MOXA_RS422;
+	} else {
+		if ((device & 0x0F00) == 0x0300) {
+			pci_warn(dev, "RS232 interface is not supported.");
+			return -EINVAL;
+		}
+	}
+	return pci_moxa_set_interface(dev, port->line, mode);
+}
+
 static int pci_moxa_init(struct pci_dev *dev)
 {
 	unsigned short device = dev->device;
@@ -1965,9 +1993,22 @@ static int pci_moxa_setup(struct serial_private *priv,
 			  struct uart_8250_port *port,
 			  int idx)
 {
+	struct pci_dev *dev = priv->dev;
+	unsigned short device = dev->device;
 	unsigned int bar = FL_GET_BASE(board->flags);
 	int offset;
 
+	/*
+	 * For the device IDs of MOXA PCIe boards match the pattern 0x*3** and 0x*1**,
+	 * these boards support switching interface between RS422/RS485 using TIOCSRS485.
+	 */
+	if ((device & 0x0F00) == 0x0100 || (device & 0x0F00) == 0x0300) {
+		port->port.rs485_config = pci_moxa_rs485_config;
+		port->port.rs485_supported = pci_moxa_rs485_supported;
+
+		if ((device & 0x0F00) == 0x0300)
+			port->port.rs485.flags = SER_RE422_ENABLED;
+	}
 	if (board->num_ports == 4 && idx == 3)
 		offset = 7 * board->uart_offset;
 	else
diff --git a/drivers/tty/serial/serial_core.c b/drivers/tty/serial/serial_core.c
index 7bdc21d5e13b..f316d9705809 100644
--- a/drivers/tty/serial/serial_core.c
+++ b/drivers/tty/serial/serial_core.c
@@ -1299,7 +1299,7 @@ static int uart_get_icount(struct tty_struct *tty,
 
 #define SER_RS485_LEGACY_FLAGS	(SER_RS485_ENABLED | SER_RS485_RTS_ON_SEND | \
 				 SER_RS485_RTS_AFTER_SEND | SER_RS485_RX_DURING_TX | \
-				 SER_RS485_TERMINATE_BUS)
+				 SER_RS485_TERMINATE_BUS | SER_RS422_ENALBED)
 
 static int uart_check_rs485_flags(struct uart_port *port, struct serial_rs485 *rs485)
 {
@@ -1365,11 +1365,23 @@ static void uart_sanitize_serial_rs485(struct uart_port *port, struct serial_rs4
 {
 	u32 supported_flags = port->rs485_supported.flags;
 
-	if (!(rs485->flags & SER_RS485_ENABLED)) {
+	if (!(rs485->flags & SER_RS485_ENABLED) && !(rs485->flags & SER_RS422_ENABLED)) {
 		memset(rs485, 0, sizeof(*rs485));
 		return;
 	}
-
+	/* Pick sane setting if the user enables both interfaces */
+	if (rs485->flags & SER_RS485_ENABLED && rs485->flags & SER_RS422_ENABLED) {
+		dev_warn_ratelimited(port->dev,
+			"%s (%d): Invalid serial interface setting, using RS485 instead\n",
+			port->name, port->line);
+		rs485->flags &= ~(SER_RS422_ENABLED);
+	}
+	/* Clear other bits and return if enalbe RS422 */
+	if (rs485->flags & SER_RS422_ENABLED) {
+		memset(rs485, 0, sizeof(*rs485));
+		rs485->flags |= SER_RS422_ENABLED;
+		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) ==
@@ -1394,7 +1406,7 @@ 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))
+	if (!(rs485->flags & SER_RS485_ENABLED) && !(rs485->flags & SER_RS422_ENABLED))
 		return;
 
 	gpiod_set_value_cansleep(port->rs485_term_gpio,
diff --git a/include/uapi/linux/serial.h b/include/uapi/linux/serial.h
index 53bc1af67a41..427609fd52cb 100644
--- a/include/uapi/linux/serial.h
+++ b/include/uapi/linux/serial.h
@@ -137,6 +137,8 @@ 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_RS422_ENABLED		- RS422 enabled.
  */
 struct serial_rs485 {
 	__u32	flags;
@@ -149,6 +151,8 @@ struct serial_rs485 {
 #define SER_RS485_ADDR_RECV		(1 << 7)
 #define SER_RS485_ADDR_DEST		(1 << 8)
 
+#define SER_RS422_ENABLED		(1 << 9)
+
 	__u32	delay_rts_before_send;
 	__u32	delay_rts_after_send;
 
-- 
2.34.1