1 files changed, 51 insertions, 0 deletions

diff --git a/drivers/tty/serial/imx.c b/drivers/tty/serial/imx.c
index f63cdd6794..8fde71138c 100644
--- a/drivers/tty/serial/imx.c
+++ b/drivers/tty/serial/imx.c
@@ -1560,6 +1560,7 @@ static void imx_uart_shutdown(struct uart_port *port)
 	struct imx_port *sport = (struct imx_port *)port;
 	unsigned long flags;
 	u32 ucr1, ucr2, ucr4, uts;
+	int loops;
 
 	if (sport->dma_is_enabled) {
 		dmaengine_terminate_sync(sport->dma_chan_tx);
@@ -1622,6 +1623,56 @@ static void imx_uart_shutdown(struct uart_port *port)
 	ucr4 &= ~UCR4_TCEN;
 	imx_uart_writel(sport, ucr4, UCR4);
 
+	/*
+	 * We have to ensure the tx state machine ends up in OFF. This
+	 * is especially important for rs485 where we must not leave
+	 * the RTS signal high, blocking the bus indefinitely.
+	 *
+	 * All interrupts are now disabled, so imx_uart_stop_tx() will
+	 * no longer be called from imx_uart_transmit_buffer(). It may
+	 * still be called via the hrtimers, and if those are in play,
+	 * we have to honour the delays.
+	 */
+	if (sport->tx_state == WAIT_AFTER_RTS || sport->tx_state == SEND)
+		imx_uart_stop_tx(port);
+
+	/*
+	 * In many cases (rs232 mode, or if tx_state was
+	 * WAIT_AFTER_RTS, or if tx_state was SEND and there is no
+	 * delay_rts_after_send), this will have moved directly to
+	 * OFF. In rs485 mode, tx_state might already have been
+	 * WAIT_AFTER_SEND and the hrtimer thus already started, or
+	 * the above imx_uart_stop_tx() call could have started it. In
+	 * those cases, we have to wait for the hrtimer to fire and
+	 * complete the transition to OFF.
+	 */
+	loops = port->rs485.flags & SER_RS485_ENABLED ?
+		port->rs485.delay_rts_after_send : 0;
+	while (sport->tx_state != OFF && loops--) {
+		uart_port_unlock_irqrestore(&sport->port, flags);
+		msleep(1);
+		uart_port_lock_irqsave(&sport->port, &flags);
+	}
+
+	if (sport->tx_state != OFF) {
+		dev_warn(sport->port.dev, "unexpected tx_state %d\n",
+			 sport->tx_state);
+		/*
+		 * This machine may be busted, but ensure the RTS
+		 * signal is inactive in order not to block other
+		 * devices.
+		 */
+		if (port->rs485.flags & SER_RS485_ENABLED) {
+			ucr2 = imx_uart_readl(sport, UCR2);
+			if (port->rs485.flags & SER_RS485_RTS_AFTER_SEND)
+				imx_uart_rts_active(sport, &ucr2);
+			else
+				imx_uart_rts_inactive(sport, &ucr2);
+			imx_uart_writel(sport, ucr2, UCR2);
+		}
+		sport->tx_state = OFF;
+	}
+
 	uart_port_unlock_irqrestore(&sport->port, flags);
 
 	clk_disable_unprepare(sport->clk_per);