tty: xuartps: Force enable the UART in xuartps_console_write

It is possible that under certain circumstances xuartps_console_write is entered
while the UART disabled. When this happens the code will busy loop in
xuartps_console_putchar, since the character is never written and the TXEMPTY
flag is never set. The result is a system lockup. This patch force enables the
UART for the duration of xuartps_console_write to avoid this.

Signed-off-by: Lars-Peter Clausen <lars@metafoo.de>
Signed-off-by: John Linn <john.linn@xilinx.com>
Signed-off-by: Michal Simek <michal.simek@xilinx.com>
Signed-off-by: Soren Brinkmann <soren.brinkmann@xilinx.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

drivers/tty/serial/xilinx_uartps.c

@@ -953,7 +953,7 @@ static void xuartps_console_write(struct console *co, const char *s,
 {
 	struct uart_port *port = &xuartps_port[co->index];
 	unsigned long flags;
-	unsigned int imr;
+	unsigned int imr, ctrl;
 	int locked = 1;
 
 	if (oops_in_progress)
@@ -965,9 +965,19 @@ static void xuartps_console_write(struct console *co, const char *s,
 	imr = xuartps_readl(XUARTPS_IMR_OFFSET);
 	xuartps_writel(imr, XUARTPS_IDR_OFFSET);
 
+	/*
+	 * Make sure that the tx part is enabled. Set the TX enable bit and
+	 * clear the TX disable bit to enable the transmitter.
+	 */
+	ctrl = xuartps_readl(XUARTPS_CR_OFFSET);
+	xuartps_writel((ctrl & ~XUARTPS_CR_TX_DIS) | XUARTPS_CR_TX_EN,
+		XUARTPS_CR_OFFSET);
+
 	uart_console_write(port, s, count, xuartps_console_putchar);
 	xuartps_console_wait_tx(port);
 
+	xuartps_writel(ctrl, XUARTPS_CR_OFFSET);
+
 	/* restore interrupt state, it seems like there may be a h/w bug
 	 * in that the interrupt enable register should not need to be
 	 * written based on the data sheet