cadence_uart: check for serial backend before using it.

This checks that s->chr is not NULL before using it.

Signed-off-by: KONRAD Frederic <fred.konrad@greensocs.com>
Reviewed-by: Peter Crosthwaite <peter.crosthwaite@xilinx.com>
Signed-off-by: Peter Maydell <peter.maydell@linaro.org>
(cherry picked from commit af52fe8)
Signed-off-by: Michael Roth <mdroth@linux.vnet.ibm.com>

hw/char/cadence_uart.c

@@ -175,8 +175,10 @@ static void uart_send_breaks(UartState *s)
 {
     int break_enabled = 1;
 
-    qemu_chr_fe_ioctl(s->chr, CHR_IOCTL_SERIAL_SET_BREAK,
-                               &break_enabled);
+    if (s->chr) {
+        qemu_chr_fe_ioctl(s->chr, CHR_IOCTL_SERIAL_SET_BREAK,
+                                   &break_enabled);
+    }
 }
 
 static void uart_parameters_setup(UartState *s)
@@ -227,7 +229,9 @@ static void uart_parameters_setup(UartState *s)
 
     packet_size += ssp.data_bits + ssp.stop_bits;
     s->char_tx_time = (get_ticks_per_sec() / ssp.speed) * packet_size;
-    qemu_chr_fe_ioctl(s->chr, CHR_IOCTL_SERIAL_SET_PARAMS, &ssp);
+    if (s->chr) {
+        qemu_chr_fe_ioctl(s->chr, CHR_IOCTL_SERIAL_SET_PARAMS, &ssp);
+    }
 }
 
 static int uart_can_receive(void *opaque)
@@ -295,6 +299,7 @@ static gboolean cadence_uart_xmit(GIOChannel *chan, GIOCondition cond,
     /* instant drain the fifo when there's no back-end */
     if (!s->chr) {
         s->tx_count = 0;
+        return FALSE;
     }
 
     if (!s->tx_count) {
@@ -374,7 +379,9 @@ static void uart_read_rx_fifo(UartState *s, uint32_t *c)
         *c = s->rx_fifo[rx_rpos];
         s->rx_count--;
 
-        qemu_chr_accept_input(s->chr);
+        if (s->chr) {
+            qemu_chr_accept_input(s->chr);
+        }
     } else {
         *c = 0;
     }