drivers: serial: uart_max32: Refactor IRQ flag clearing

api_irq_update was clearing TX interrupt flags before the TX interrupt
could be served, breaking synchronization in time-sensitive applications.

Changes:
1. Remove unnecessary MXC_UART_ClearFlags() calls in api_fifo_read() and
   api_irq_update to avoid premature flag clearing; ISR handler already
   clears them after returning from the callback.
2. Replace raw flag checks in irq_is_pending() with more complete
   api_irq_rx_ready() and api_irq_tx_ready().

Signed-off-by: Tahsin Mutlugun <[email protected]>

Author: ttmut

drivers/serial/uart_max32.c

@@ -367,9 +367,6 @@ static int api_fifo_read(const struct device *dev, uint8_t *rx_data, const int s
 	const struct max32_uart_config *cfg = dev->config;
 
 	num_rx = MXC_UART_ReadRXFIFO(cfg->regs, (unsigned char *)rx_data, size);
-	if (num_rx == 0) {
-		MXC_UART_ClearFlags(cfg->regs, ADI_MAX32_UART_INT_RX);
-	}
 
 	return num_rx;
 }
@@ -438,9 +435,7 @@ static void api_irq_err_disable(const struct device *dev)
 
 static int api_irq_is_pending(const struct device *dev)
 {
-	struct max32_uart_data *const data = dev->data;
-
-	return (data->flags & (ADI_MAX32_UART_INT_RX | ADI_MAX32_UART_INT_TX));
+	return api_irq_rx_ready(dev) || api_irq_tx_ready(dev);
 }
 
 static int api_irq_update(const struct device *dev)
@@ -451,8 +446,6 @@ static int api_irq_update(const struct device *dev)
 	data->flags = MXC_UART_GetFlags(cfg->regs);
 	data->status = MXC_UART_GetStatus(cfg->regs);
 
-	MXC_UART_ClearFlags(cfg->regs, data->flags);
-
 	return 1;
 }