hw/char: cadence_uart: Move clock/reset check to uart_can_receive()

Currently the clock/reset check is done in uart_receive(), but we
can move the check to uart_can_receive() which is earlier.

Signed-off-by: Bin Meng <bmeng.cn@gmail.com>
Reviewed-by: Edgar E. Iglesias <edgar.iglesias@xilinx.com>
Reviewed-by: Alistair Francis <alistair.francis@wdc.com>
Message-id: 20210901124521.30599-4-bmeng.cn@gmail.com
Signed-off-by: Peter Maydell <peter.maydell@linaro.org>

hw/char/cadence_uart.c

@@ -235,8 +235,16 @@ static void uart_parameters_setup(CadenceUARTState *s)
 static int uart_can_receive(void *opaque)
 {
     CadenceUARTState *s = opaque;
-    int ret = MAX(CADENCE_UART_RX_FIFO_SIZE, CADENCE_UART_TX_FIFO_SIZE);
-    uint32_t ch_mode = s->r[R_MR] & UART_MR_CHMODE;
+    int ret;
+    uint32_t ch_mode;
+
+    /* ignore characters when unclocked or in reset */
+    if (!clock_is_enabled(s->refclk) || device_is_in_reset(DEVICE(s))) {
+        return 0;
+    }
+
+    ret = MAX(CADENCE_UART_RX_FIFO_SIZE, CADENCE_UART_TX_FIFO_SIZE);
+    ch_mode = s->r[R_MR] & UART_MR_CHMODE;
 
     if (ch_mode == NORMAL_MODE || ch_mode == ECHO_MODE) {
         ret = MIN(ret, CADENCE_UART_RX_FIFO_SIZE - s->rx_count);
@@ -358,11 +366,6 @@ static void uart_receive(void *opaque, const uint8_t *buf, int size)
     CadenceUARTState *s = opaque;
     uint32_t ch_mode = s->r[R_MR] & UART_MR_CHMODE;
 
-    /* ignore characters when unclocked or in reset */
-    if (!clock_is_enabled(s->refclk) || device_is_in_reset(DEVICE(s))) {
-        return;
-    }
-
     if (ch_mode == NORMAL_MODE || ch_mode == ECHO_MODE) {
         uart_write_rx_fifo(opaque, buf, size);
     }