serial: qcom-geni: Enable support for half-duplex mode

Enable the use of the RTS pin for direction control in half-duplex modes to
prevent data collisions. Utilize the rs485 structure and callbacks in the
serial core framework to support half-duplex modes. Implement support for
the TIOCSRS485 IOCTL value and the struct serial_rs485.

Signed-off-by: Anup Kulkarni <[e-mail]>
Link: https://lore.kernel.org/r/[e-mail]
Signed-off-by: Greg Kroah-Hartman <[e-mail]>

drivers/tty/serial/qcom_geni_serial.c

···
 	},
 };
 
+static const struct serial_rs485 qcom_geni_rs485_supported = {
+	.flags = SER_RS485_ENABLED | SER_RS485_RTS_AFTER_SEND | SER_RS485_RTS_ON_SEND,
+};
+
+/**
+ * qcom_geni_set_rs485_mode - Set RTS pin state for RS485 mode
+ * @uport: UART port
+ * @flag: RS485 flag to determine RTS polarity
+ *
+ * Enables manual RTS control for RS485. Sets RTS to READY or NOT_READY
+ * based on the specified flag if RS485 mode is enabled.
+ */
+static void qcom_geni_set_rs485_mode(struct uart_port *uport, u32 flag)
+{
+	if (!(uport->rs485.flags & SER_RS485_ENABLED))
+		return;
+
+	u32 rfr = UART_MANUAL_RFR_EN;
+
+	if (uport->rs485.flags & flag)
+		rfr |= UART_RFR_NOT_READY;
+	else
+		rfr |= UART_RFR_READY;
+
+	writel(rfr, uport->membase + SE_UART_MANUAL_RFR);
+}
+
 static int qcom_geni_serial_request_port(struct uart_port *uport)
 {
 	struct platform_device *pdev = to_platform_device(uport->dev);
···
 	xmit_size = kfifo_out_linear_ptr(&tport->xmit_fifo, &tail,
 			UART_XMIT_SIZE);
 
+	qcom_geni_set_rs485_mode(uport, SER_RS485_RTS_ON_SEND);
+
 	qcom_geni_serial_setup_tx(uport, xmit_size);
 
 	ret = geni_se_tx_dma_prep(&port->se, tail, xmit_size,
···
 	}
 
 	if (dma) {
-		if (dma_tx_status & TX_DMA_DONE)
+		if (dma_tx_status & TX_DMA_DONE) {
 			qcom_geni_serial_handle_tx_dma(uport);
+			qcom_geni_set_rs485_mode(uport, SER_RS485_RTS_AFTER_SEND);
+	}
 
 		if (dma_rx_status) {
 			if (dma_rx_status & RX_RESET_DONE)
···
 	}
 }
 
+/**
+ * qcom_geni_rs485_config - Configure RS485 settings for the UART port
+ * @uport: Pointer to the UART port structure
+ * @termios: Pointer to the termios structure
+ * @rs485: Pointer to the RS485 configuration structure
+ * This function configures the RTS (Request to Send) pin behavior for RS485 mode.
+ * When RS485 mode is enabled, the RTS pin is kept in default ACTIVE HIGH state.
+ * Return: Always returns 0.
+ */
+
+static int qcom_geni_rs485_config(struct uart_port *uport,
+				  struct ktermios *termios, struct serial_rs485 *rs485)
+{
+	qcom_geni_set_rs485_mode(uport, SER_RS485_ENABLED);
+
+	return 0;
+}
+
 static const struct uart_ops qcom_geni_console_pops = {
 	.tx_empty = qcom_geni_serial_tx_empty,
 	.stop_tx = qcom_geni_serial_stop_tx_fifo,
···
 		return -EINVAL;
 	uport->mapbase = res->start;
 
+	uport->rs485_config = qcom_geni_rs485_config;
+	uport->rs485_supported = qcom_geni_rs485_supported;
 	port->tx_fifo_depth = DEF_FIFO_DEPTH_WORDS;
 	port->rx_fifo_depth = DEF_FIFO_DEPTH_WORDS;
 	port->tx_fifo_width = DEF_FIFO_WIDTH_BITS;
···
 		dev_err(uport->dev, "Failed to get IRQ ret %d\n", ret);
 		return ret;
 	}
+
+	ret = uart_get_rs485_mode(uport);
+	if (ret)
+		return ret;
 
 	ret = uart_add_one_port(drv, uport);
 	if (ret)