[PATCH v2 13/15] serial: 8250_mxpcie: add break support for RS485 using MUEx50 features

[Crescent Hsieh <crescentcy.hsieh@moxa.com>]

On MUEx50, break signaling under RS485 requires a driver-specific
sequence and cannot be handled correctly by the generic 8250 break
implementation alone.

Implement a mxpcie break_ctl callback that performs MUEx50-specific
break handling when RS485 is enabled and fall back to the default 8250
break handling for other modes.

Signed-off-by: Crescent Hsieh <crescentcy.hsieh@moxa.com>
---
 drivers/tty/serial/8250/8250_mxpcie.c | 49 +++++++++++++++++++++++++++
 1 file changed, 49 insertions(+)

diff --git a/drivers/tty/serial/8250/8250_mxpcie.c b/drivers/tty/serial/8250/8250_mxpcie.c
index db2b9a972a50..da81ea7970f0 100644
--- a/drivers/tty/serial/8250/8250_mxpcie.c
+++ b/drivers/tty/serial/8250/8250_mxpcie.c
@@ -53,6 +53,7 @@
 
 /* Special Function Register (SFR) */
 #define MOXA_PUART_SFR		0x07
+#define MOXA_PUART_SFR_FORCE_TX	BIT(0)
 #define MOXA_PUART_SFR_950	BIT(5)
 
 /* Enhanced Function Register (EFR) */
@@ -427,6 +428,53 @@ static int mxpcie8250_handle_irq(struct uart_port *port)
 	return 1;
 }
 
+static void mxpcie8250_software_break_ctl(struct uart_port *port, int break_state)
+{
+	struct uart_8250_port *up = up_to_u8250p(port);
+	struct tty_struct *tty = port->state->port.tty;
+	unsigned char tx_byte = 0x01;
+	unsigned int baud, quot;
+	u8 sfr;
+
+	guard(uart_port_lock_irqsave)(port);
+
+	if (break_state == -1) {
+		serial_out(up, UART_LCR, up->lcr | UART_LCR_DLAB);
+		serial_dl_write(up, 0);
+		serial_out(up, UART_LCR, up->lcr);
+
+		serial_out(up, MOXA_PUART_TX_FIFO_MEM, tx_byte);
+
+		sfr = serial_in(up, MOXA_PUART_SFR);
+		serial_out(up, MOXA_PUART_SFR, sfr | MOXA_PUART_SFR_FORCE_TX);
+
+		up->lcr |= UART_LCR_SBC;
+		serial_out(up, UART_LCR, up->lcr);
+	} else {
+		up->lcr &= ~UART_LCR_SBC;
+		serial_out(up, UART_LCR, up->lcr);
+
+		sfr = serial_in(up, MOXA_PUART_SFR);
+		serial_out(up, MOXA_PUART_SFR, sfr & ~MOXA_PUART_SFR_FORCE_TX);
+
+		serial_out(up, UART_FCR, UART_FCR_CLEAR_XMIT);
+
+		baud = tty_get_baud_rate(tty);
+		quot = uart_get_divisor(port, baud);
+		serial8250_do_set_divisor(port, baud, quot);
+		serial_out(up, UART_LCR, up->lcr);
+	}
+}
+
+static void mxpcie8250_break_ctl(struct uart_port *port, int break_state)
+{
+	if (port->rs485.flags & SER_RS485_ENABLED &&
+	    !(port->rs485.flags & SER_RS485_MODE_RS422))
+		mxpcie8250_software_break_ctl(port, break_state);
+	else
+		serial8250_do_break_ctl(port, break_state);
+}
+
 static void mxpcie8250_work_handler(struct work_struct *work)
 {
 	struct mxpcie8250_port *priv_port = container_of(work, struct mxpcie8250_port, work);
@@ -540,6 +588,7 @@ static int mxpcie8250_probe(struct pci_dev *pdev, const struct pci_device_id *id
 	up.port.throttle = mxpcie8250_throttle;
 	up.port.unthrottle = mxpcie8250_unthrottle;
 	up.port.handle_irq = mxpcie8250_handle_irq;
+	up.port.break_ctl = mxpcie8250_break_ctl;
 
 	for (unsigned int i = 0; i < num_ports; i++) {
 		mxpcie8250_setup_port(pdev, priv, &up, i);
-- 
2.45.2