drivers: mspi_dw: Remove needless TXEIR check

This is a follow-up to commit f0f5f8c.

There is no need to check if TXE interrupt flag is set before
calling tx_dummy_bytes(), as the function can handle the case
when it is called even though there is no room in the TX FIFO.
On the other hand, the check may be actually harmful, as it may
prevent adding more items to the TX FIFO while the SSI controller
is waiting until the FIFO achieves its transfer start level.

Signed-off-by: Andrzej Głąbek <[email protected]>

Author: anangl

drivers/mspi/mspi_dw.c

@@ -209,6 +209,8 @@ static bool tx_dummy_bytes(const struct device *dev)
 	 * FIFO to avoid overflowing it; `max_queued_dummy_bytes` accounts
 	 * that one byte that can be partially received, thus not included
 	 * in the value from the RXFLR register.
+	 * This check also handles the case when the function is called but
+	 * the TX FIFO is already filled up (fifo_room == 0).
 	 */
 	if (fifo_room <= rx_fifo_items) {
 		return false;
@@ -363,8 +365,15 @@ static void handle_fifos(const struct device *dev)
 				break;
 			}
 
-			if (dev_data->dummy_bytes == 0 ||
-			    !(int_status & RISR_TXEIR_BIT)) {
+			/* If there are still some dummy bytes to transmit,
+			 * always try to put some into the TX FIFO, no matter
+			 * what's the TXE interrupt status (the TX FIFO may be
+			 * filled over its threshold level, hence its interrupt
+			 * flag will not be set, but below its transmit level,
+			 * so the controller may be waiting for more items to
+			 * appear there).
+			 */
+			if (dev_data->dummy_bytes == 0) {
 				break;
 			}