linux-kernel - [PATCH 1/2 bugfix] serial: imx: reset the uart port all the time

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Date:	Wed, 21 May 2014 08:56:28 +0800
From:	Huang Shijie <b32955@...escale.com>
To:	<gregkh@...uxfoundation.org>
CC:	<linux-serial@...r.kernel.org>,
	<linux-arm-kernel@...ts.infradead.org>,
	<linux-kernel@...r.kernel.org>, Huang Shijie <b32955@...escale.com>
Subject: [PATCH 1/2 bugfix] serial: imx: reset the uart port all the time

Current code resets the uart port only when it supports the irda mode.
In actually, we also need to reset the uart port in the non-irda mode.
A hang was caught in the following case:

    UART A transmits data to the other end. But the transmission maybe
    terminated. In some corner case, the TX FIFO maybe not empty.

The kernel will hang at the imx_set_termios():
	............................................................
	while (!(readl(sport->port.membase + USR2) & USR2_TXDC))
		barrier();
	............................................................

This patch resets the uart port all the time in the imx_startup().
And fix the hang.

Signed-off-by: Huang Shijie <b32955@...escale.com>
---
 drivers/tty/serial/imx.c |   22 ++++++++++------------
 1 files changed, 10 insertions(+), 12 deletions(-)

diff --git a/drivers/tty/serial/imx.c b/drivers/tty/serial/imx.c
index 3b6c1a2..64901d0 100644
--- a/drivers/tty/serial/imx.c
+++ b/drivers/tty/serial/imx.c
@@ -1070,7 +1070,7 @@ static void imx_disable_dma(struct imx_port *sport)
 static int imx_startup(struct uart_port *port)
 {
 	struct imx_port *sport = (struct imx_port *)port;
-	int retval;
+	int retval, i;
 	unsigned long flags, temp;
 
 	retval = clk_prepare_enable(sport->clk_per);
@@ -1098,17 +1098,15 @@ static int imx_startup(struct uart_port *port)
 
 	writel(temp & ~UCR4_DREN, sport->port.membase + UCR4);
 
-	if (USE_IRDA(sport)) {
-		/* reset fifo's and state machines */
-		int i = 100;
-		temp = readl(sport->port.membase + UCR2);
-		temp &= ~UCR2_SRST;
-		writel(temp, sport->port.membase + UCR2);
-		while (!(readl(sport->port.membase + UCR2) & UCR2_SRST) &&
-		    (--i > 0)) {
-			udelay(1);
-		}
-	}
+	/* Reset fifo's and state machines */
+	i = 100;
+
+	temp = readl(sport->port.membase + UCR2);
+	temp &= ~UCR2_SRST;
+	writel(temp, sport->port.membase + UCR2);
+
+	while (!(readl(sport->port.membase + UCR2) & UCR2_SRST) && (--i > 0))
+		udelay(1);
 
 	/*
 	 * Allocate the IRQ(s) i.MX1 has three interrupts whereas later
-- 
1.7.8

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