[PATCH 4.9 075/121] serial: uartps: Add a timeout to the tx empty wait

[Greg Kroah-Hartman]

From: Shubhrajyoti Datta <shubhrajyoti.datta@xxxxxxxxxx>

commit 277375b864e8147975b064b513f491e2a910e66a upstream.

In case the cable is not connected then the target gets into
an infinite wait for tx empty.
Add a timeout to the tx empty wait.

Reported-by: Jean-Francois Dagenais <jeff.dagenais@xxxxxxxxx>
Signed-off-by: Shubhrajyoti Datta <shubhrajyoti.datta@xxxxxxxxxx>
Signed-off-by: Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx>
Signed-off-by: Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx>

---
 drivers/tty/serial/xilinx_uartps.c |   14 ++++++++++----
 1 file changed, 10 insertions(+), 4 deletions(-)

--- a/drivers/tty/serial/xilinx_uartps.c
+++ b/drivers/tty/serial/xilinx_uartps.c
@@ -30,6 +30,7 @@
 #include <linux/io.h>
 #include <linux/of.h>
 #include <linux/module.h>
+#include <linux/iopoll.h>
 
 #define CDNS_UART_TTY_NAME	"ttyPS"
 #define CDNS_UART_NAME		"xuartps"
@@ -38,6 +39,7 @@
 #define CDNS_UART_NR_PORTS	2
 #define CDNS_UART_FIFO_SIZE	64	/* FIFO size */
 #define CDNS_UART_REGISTER_SPACE	0x1000
+#define TX_TIMEOUT		500000
 
 /* Rx Trigger level */
 static int rx_trigger_level = 56;
@@ -681,16 +683,20 @@ static void cdns_uart_set_termios(struct
 	unsigned int cval = 0;
 	unsigned int baud, minbaud, maxbaud;
 	unsigned long flags;
-	unsigned int ctrl_reg, mode_reg;
+	unsigned int ctrl_reg, mode_reg, val;
+	int err;
 
 	spin_lock_irqsave(&port->lock, flags);
 
 	/* Wait for the transmit FIFO to empty before making changes */
 	if (!(readl(port->membase + CDNS_UART_CR) &
 				CDNS_UART_CR_TX_DIS)) {
-		while (!(readl(port->membase + CDNS_UART_SR) &
-				CDNS_UART_SR_TXEMPTY)) {
-			cpu_relax();
+		err = readl_poll_timeout(port->membase + CDNS_UART_SR,
+					 val, (val & CDNS_UART_SR_TXEMPTY),
+					 1000, TX_TIMEOUT);
+		if (err) {
+			dev_err(port->dev, "timed out waiting for tx empty");
+			return;
 		}
 	}