[PATCH/RFC 3/3] tty: Add software emulated RS485 support for 8250

["Matwey V. Kornilov" <matwey@xxxxxxxxxx>]

Implementation of software emulation of RS485 direction handling is based on omap-serial driver.
It is acts as the following. At transmission start, RTS is set (if required) and receiver is off (if required).
At transmission stop, RTS is set (if required) and fifo is flushed.

Signed-off-by: Matwey V. Kornilov <matwey@xxxxxxxxxx>
---
 drivers/tty/serial/8250/8250_port.c | 32 ++++++++++++++++++++++++++++++++
 1 file changed, 32 insertions(+)

diff --git a/drivers/tty/serial/8250/8250_port.c b/drivers/tty/serial/8250/8250_port.c
index 0bbf340..1c098d7 100644
--- a/drivers/tty/serial/8250/8250_port.c
+++ b/drivers/tty/serial/8250/8250_port.c
@@ -559,7 +559,37 @@ static void serial8250_rpm_put_tx(struct uart_8250_port *p)
 	pm_runtime_mark_last_busy(p->port.dev);
 	pm_runtime_put_autosuspend(p->port.dev);
 }
+static void serial8250_stop_rx(struct uart_port *port);
+static void serial8250_rs485_start_tx(struct uart_8250_port *p)
+{
+	if (p->capabilities & UART_CAP_HW485 || !(p->port.rs485.flags & SER_RS485_ENABLED))
+		return;
+
+	if (p->port.rs485.flags & SER_RS485_RTS_ON_SEND) {
+		serial_port_out(&p->port, UART_MCR, UART_MCR_RTS);
+		if (p->port.rs485.delay_rts_before_send > 0)
+			mdelay(p->port.rs485.delay_rts_before_send);
+	}
+	if (!(p->port.rs485.flags & SER_RS485_RX_DURING_TX))
+		serial8250_stop_rx(&p->port);
+}
+static void serial8250_rs485_stop_tx(struct uart_8250_port *p)
+{
+	if (p->capabilities & UART_CAP_HW485 || !(p->port.rs485.flags & SER_RS485_ENABLED))
+		return;
 
+	if (p->port.rs485.flags & SER_RS485_RTS_AFTER_SEND) {
+		if (p->port.rs485.delay_rts_after_send > 0)
+			mdelay(p->port.rs485.delay_rts_after_send);
+		serial_port_out(&p->port, UART_MCR, UART_MCR_RTS);
+	}
+	/*
+	* Empty the RX FIFO, we are not interested in anything
+	* received during the half-duplex transmission.
+	*/
+	if (!(p->port.rs485.flags & SER_RS485_RX_DURING_TX))
+		serial8250_clear_fifos(p);
+}
 /*
  * IER sleep support.  UARTs which have EFRs need the "extended
  * capability" bit enabled.  Note that on XR16C850s, we need to
@@ -1303,6 +1333,7 @@ static void serial8250_stop_tx(struct uart_port *port)
 		up->acr |= UART_ACR_TXDIS;
 		serial_icr_write(up, UART_ACR, up->acr);
 	}
+	serial8250_rs485_stop_tx(up);
 	serial8250_rpm_put(up);
 }
 
@@ -1311,6 +1342,7 @@ static void serial8250_start_tx(struct uart_port *port)
 	struct uart_8250_port *up = up_to_u8250p(port);
 
 	serial8250_rpm_get_tx(up);
+	serial8250_rs485_start_tx(up);
 
 	if (up->dma && !up->dma->tx_dma(up))
 		return;
-- 
2.6.0

--
To unsubscribe from this list: send the line "unsubscribe linux-serial" in
the body of a message to majordomo@xxxxxxxxxxxxxxx
More majordomo info at  http://vger.kernel.org/majordomo-info.html