[nrf fromtree] drivers: mspi_dw: Add support for RX dummy cycles in single line mode

Support for 8 dummy cycles in a single line RX transaction is required
for the standard JEDEC Read SFDP command. The SSI controller does not
support dummy cycles in Standard SPI mode, but the driver can simulate
those by just sending a dummy data byte.

Signed-off-by: Andrzej Głąbek <[email protected]>
(cherry picked from commit e787296)

Author: anangl

drivers/mspi/mspi_dw.c

@@ -844,13 +844,16 @@ static int start_next_packet(const struct device *dev, k_timeout_t timeout)
 		    (dev_data->xfer.cmd_length != 0 ||
 		     dev_data->xfer.addr_length != 0)) {
 			uint32_t rx_total_bytes;
+			uint32_t dummy_cycles = dev_data->xfer.rx_dummy;
 
 			dev_data->bytes_to_discard = dev_data->xfer.cmd_length
-						   + dev_data->xfer.addr_length;
+						   + dev_data->xfer.addr_length
+						   + dummy_cycles / 8;
 			rx_total_bytes = dev_data->bytes_to_discard
 				       + packet->num_bytes;
 
-			dev_data->dummy_bytes = packet->num_bytes;
+			dev_data->dummy_bytes = dummy_cycles / 8
+					      + packet->num_bytes;
 
 			imr = IMR_TXEIM_BIT | IMR_RXFIM_BIT;
 			tmod = CTRLR0_TMOD_TX_RX;
@@ -862,11 +865,13 @@ static int start_next_packet(const struct device *dev, k_timeout_t timeout)
 			tmod = CTRLR0_TMOD_RX;
 			rx_fifo_threshold = MIN(packet_frames - 1,
 						dev_config->rx_fifo_threshold);
+
+			dev_data->spi_ctrlr0 |=
+				FIELD_PREP(SPI_CTRLR0_WAIT_CYCLES_MASK,
+					   dev_data->xfer.rx_dummy);
 		}
 
 		dev_data->ctrlr0 |= FIELD_PREP(CTRLR0_TMOD_MASK, tmod);
-		dev_data->spi_ctrlr0 |= FIELD_PREP(SPI_CTRLR0_WAIT_CYCLES_MASK,
-						   dev_data->xfer.rx_dummy);
 
 		write_rxftlr(dev, FIELD_PREP(RXFTLR_RFT_MASK,
 					     rx_fifo_threshold));
@@ -1039,10 +1044,15 @@ static int _api_transceive(const struct device *dev,
 		return -EINVAL;
 	}
 
-	if (dev_data->standard_spi &&
-	    (req->rx_dummy != 0 || req->tx_dummy != 0)) {
-		LOG_ERR("Dummy cycles unsupported in single line mode");
-		return -EINVAL;
+	if (dev_data->standard_spi) {
+		if (req->tx_dummy) {
+			LOG_ERR("TX dummy cycles unsupported in single line mode");
+			return -EINVAL;
+		}
+		if (req->rx_dummy % 8) {
+			LOG_ERR("Unsupported RX (%u) dummy cycles", req->rx_dummy);
+			return -EINVAL;
+		}
 	} else if (req->rx_dummy > SPI_CTRLR0_WAIT_CYCLES_MAX ||
 		   req->tx_dummy > SPI_CTRLR0_WAIT_CYCLES_MAX) {
 		LOG_ERR("Unsupported RX (%u) or TX (%u) dummy cycles",