drivers/serial: imx: dismiss noisy IRQ events

Converging to the upstream implementation further, disregard any event
which source is disabled, to help dealing with transitory states of
the hardware (e.g. as triggered by device closure).
Signed-off-by: Philippe Gerum <rpm@xenomai.org>
Signed-off-by: Jan Kiszka <jan.kiszka@siemens.com>

kernel/drivers/serial/rt_imx_uart.c

@@ -463,8 +463,7 @@ static int rt_imx_uart_int(rtdm_irq_t *irq_context)
 	uint64_t timestamp = rtdm_clock_read();
 	struct rt_imx_uart_ctx *ctx;
 	unsigned int usr1, usr2, ucr1;
-	int rbytes = 0;
-	int events = 0;
+	int rbytes = 0, events = 0;
 	int ret = RTDM_IRQ_NONE;
 
 	ctx = rtdm_irq_get_arg(irq_context, struct rt_imx_uart_ctx);
@@ -479,15 +478,18 @@ static int rt_imx_uart_int(rtdm_irq_t *irq_context)
 	 * Read if there is data available
 	 */
 	if (usr1 & USR1_RRDY) {
-		rbytes += rt_imx_uart_rx_chars(ctx, &timestamp);
+		if (likely(ucr1 & UCR1_RRDYEN)) {
+			rbytes = rt_imx_uart_rx_chars(ctx, &timestamp);
 			events |= RTSER_EVENT_RXPEND;
+		}
 		ret = RTDM_IRQ_HANDLED;
 	}
 
 	/*
 	 * Send data if there is data to be sent
 	 */
-	if ((usr1 & USR1_TRDY) && (ucr1 & UCR1_TXMPTYEN)) {
+	if (usr1 & USR1_TRDY) {
+		if (likely(ucr1 & UCR1_TXMPTYEN))
 			rt_imx_uart_tx_chars(ctx);
 		ret = RTDM_IRQ_HANDLED;
 	}