serial: uartps: Fix suspend functionality

The driver's suspend/resume functions were buggy.
If UART node contains any child node in the DT and
the child is established a communication path with
the parent UART. The relevant /dev/ttyPS* node will
be not available for other operations.
If the driver is trying to do any operations like
suspend/resume without checking the tty->dev status
it leads to the kernel crash/hang.

This patch fix this issue by call the device_may_wake()
with the generic parameter of type struct device.
in the uart suspend and resume paths.

It also fixes a race condition in the uart suspend
path(i.e uart_suspend_port() should be called at the
end of cdns_uart_suspend API this path updates the same)
Signed-off-by: Nava kishore Manne <navam@xilinx.com>
Signed-off-by: Michal Simek <michal.simek@xilinx.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

drivers/tty/serial/xilinx_uartps.c

@@ -1273,24 +1273,11 @@ static struct uart_driver cdns_uart_uart_driver = {
 static int cdns_uart_suspend(struct device *device)
 {
 	struct uart_port *port = dev_get_drvdata(device);
-	struct tty_struct *tty;
-	struct device *tty_dev;
-	int may_wake = 0;
-
-	/* Get the tty which could be NULL so don't assume it's valid */
-	tty = tty_port_tty_get(&port->state->port);
-	if (tty) {
-		tty_dev = tty->dev;
-		may_wake = device_may_wakeup(tty_dev);
-		tty_kref_put(tty);
-	}
+	int may_wake;
 
-	/*
-	 * Call the API provided in serial_core.c file which handles
-	 * the suspend.
-	 */
-	uart_suspend_port(&cdns_uart_uart_driver, port);
-	if (!(console_suspend_enabled && !may_wake)) {
+	may_wake = device_may_wakeup(device);
+
+	if (console_suspend_enabled && may_wake) {
 		unsigned long flags = 0;
 
 		spin_lock_irqsave(&port->lock, flags);
@@ -1305,7 +1292,11 @@ static int cdns_uart_suspend(struct device *device)
 		spin_unlock_irqrestore(&port->lock, flags);
 	}
 
-	return 0;
+	/*
+	 * Call the API provided in serial_core.c file which handles
+	 * the suspend.
+	 */
+	return uart_suspend_port(&cdns_uart_uart_driver, port);
 }
 
 /**
@@ -1319,17 +1310,9 @@ static int cdns_uart_resume(struct device *device)
 	struct uart_port *port = dev_get_drvdata(device);
 	unsigned long flags = 0;
 	u32 ctrl_reg;
-	struct tty_struct *tty;
-	struct device *tty_dev;
-	int may_wake = 0;
-
-	/* Get the tty which could be NULL so don't assume it's valid */
-	tty = tty_port_tty_get(&port->state->port);
-	if (tty) {
-		tty_dev = tty->dev;
-		may_wake = device_may_wakeup(tty_dev);
-		tty_kref_put(tty);
-	}
+	int may_wake;
+
+	may_wake = device_may_wakeup(device);
 
 	if (console_suspend_enabled && !may_wake) {
 		struct cdns_uart *cdns_uart = port->private_data;