drivers: spi: mcux_flexcomm: use rxignore bit instead of dummy read.

when no rx data need to be read set the rxignore bits.
with this change the dma setup is faster and no unnecessary
dummy writes are done to memory.

Signed-off-by: Johan Carlsson <[email protected]>

Author: Johan Carlsson

drivers/spi/spi_mcux_flexcomm.c

@@ -298,9 +298,6 @@ static int spi_mcux_configure(const struct device *dev,
 }
 
 #ifdef CONFIG_SPI_MCUX_FLEXCOMM_DMA
-/* Dummy buffer used as a sink when rc buf is null */
-uint32_t dummy_rx_buffer;
-
 /* This function is executed in the interrupt context */
 static void spi_mcux_dma_callback(const struct device *dev, void *arg,
 			 uint32_t channel, int status)
@@ -336,7 +333,7 @@ static void spi_mcux_dma_callback(const struct device *dev, void *arg,
 
 static void spi_mcux_prepare_txlastword(uint32_t *txLastWord,
 				const uint8_t *buf, const struct spi_config *spi_cfg,
-				size_t len)
+				size_t len, bool rx_ignore)
 {
 	uint32_t word_size;
 
@@ -349,6 +346,10 @@ static void spi_mcux_prepare_txlastword(uint32_t *txLastWord,
 		*txLastWord = buf[len - 1U];
 	}
 
+	if (rx_ignore) {
+		*txLastWord |= (uint32_t)SPI_FIFOWR_RXIGNORE_MASK;
+	}
+
 	*txLastWord |= (uint32_t)SPI_FIFOWR_EOT_MASK;
 
 	*txLastWord |= ((uint32_t)SPI_DEASSERT_ALL &
@@ -359,7 +360,8 @@ static void spi_mcux_prepare_txlastword(uint32_t *txLastWord,
 }
 
 static void spi_mcux_prepare_txdummy(uint32_t *dummy, bool last_packet,
-				const struct spi_config *spi_cfg)
+				     const struct spi_config *spi_cfg,
+				     bool rx_ignore)
 {
 	uint32_t word_size;
 
@@ -368,6 +370,9 @@ static void spi_mcux_prepare_txdummy(uint32_t *dummy, bool last_packet,
 	if (last_packet) {
 		*dummy |= (uint32_t)SPI_FIFOWR_EOT_MASK;
 	}
+	if (rx_ignore) {
+		*dummy |= (uint32_t)SPI_FIFOWR_RXIGNORE_MASK;
+	}
 
 	*dummy |= ((uint32_t)SPI_DEASSERT_ALL &
 				(~(uint32_t)SPI_DEASSERTNUM_SSEL((uint32_t)spi_cfg->slave)));
@@ -377,7 +382,8 @@ static void spi_mcux_prepare_txdummy(uint32_t *dummy, bool last_packet,
 }
 
 static int spi_mcux_dma_tx_load(const struct device *dev, const uint8_t *buf,
-				 const struct spi_config *spi_cfg, size_t len, bool last_packet)
+				const struct spi_config *spi_cfg, size_t len,
+				bool last_packet, bool rx_ignore)
 {
 	const struct spi_mcux_config *cfg = dev->config;
 	struct spi_mcux_data *data = dev->data;
@@ -400,11 +406,11 @@ static int spi_mcux_dma_tx_load(const struct device *dev, const uint8_t *buf,
 	if (buf == NULL) {
 		data->dummy_tx_buffer = 0;
 		data->last_word = 0;
-		spi_mcux_prepare_txdummy(&data->dummy_tx_buffer, last_packet, spi_cfg);
+		spi_mcux_prepare_txdummy(&data->dummy_tx_buffer, last_packet, spi_cfg, rx_ignore);
 
 		if (last_packet  &&
 		    ((word_size > 8) ? (len > 2U) : (len > 1U))) {
-			spi_mcux_prepare_txdummy(&data->last_word, last_packet, spi_cfg);
+			spi_mcux_prepare_txdummy(&data->last_word, last_packet, spi_cfg, rx_ignore);
 			blk_cfg->source_address = (uint32_t)&data->dummy_tx_buffer;
 			blk_cfg->dest_address = (uint32_t)&base->FIFOWR;
 			blk_cfg->block_size = (word_size > 8) ?
@@ -433,7 +439,7 @@ static int spi_mcux_dma_tx_load(const struct device *dev, const uint8_t *buf,
 		}
 	} else {
 		if (last_packet) {
-			spi_mcux_prepare_txlastword(&data->last_word, buf, spi_cfg, len);
+			spi_mcux_prepare_txlastword(&data->last_word, buf, spi_cfg, len, rx_ignore);
 		}
 		/* If last packet and data transfer frame is bigger then 1,
 		 * use dma descriptor to send the last data.
@@ -481,7 +487,7 @@ static int spi_mcux_dma_tx_load(const struct device *dev, const uint8_t *buf,
 
 	uint32_t tmpData = 0U;
 
-	spi_mcux_prepare_txdummy(&tmpData, last_packet, spi_cfg);
+	spi_mcux_prepare_txdummy(&tmpData, last_packet, spi_cfg, rx_ignore);
 
 	/* Setup the control info.
 	 * Halfword writes to just the control bits (offset 0xE22) doesn't push
@@ -514,21 +520,19 @@ static int spi_mcux_dma_rx_load(const struct device *dev, uint8_t *buf,
 	/* retrieve active RX DMA channel (used in callback) */
 	struct stream *stream = &data->dma_rx;
 
+	if (buf == NULL) {
+		data->status_flags |= SPI_MCUX_FLEXCOMM_DMA_RX_DONE_FLAG;
+		return 0;
+	}
+
 	blk_cfg = &stream->dma_blk_cfg[0];
 
 	/* prepare the block for this RX DMA channel */
 	memset(blk_cfg, 0, sizeof(struct dma_block_config));
 	blk_cfg->block_size = len;
 
 	/* rx direction has periph as source and mem as dest. */
-	if (buf == NULL) {
-		/* if rx buff is null, then write data to dummy address. */
-		blk_cfg->dest_address = (uint32_t)&dummy_rx_buffer;
-		blk_cfg->dest_addr_adj = DMA_ADDR_ADJ_NO_CHANGE;
-	} else {
-		blk_cfg->dest_address = (uint32_t)buf;
-	}
-
+	blk_cfg->dest_address = (uint32_t)buf;
 	blk_cfg->source_address = (uint32_t)&base->FIFORD;
 
 	/* direction is given by the DT */
@@ -554,6 +558,7 @@ static int spi_mcux_dma_move_buffers(const struct device *dev, size_t len,
 			const struct spi_config *spi_cfg, bool last_packet)
 {
 	struct spi_mcux_data *data = dev->data;
+	bool rx_ignore = data->ctx.rx_buf ? false : true;
 	int ret;
 
 	ret = spi_mcux_dma_rx_load(dev, data->ctx.rx_buf, len);
@@ -563,7 +568,7 @@ static int spi_mcux_dma_move_buffers(const struct device *dev, size_t len,
 	}
 
 	ret = spi_mcux_dma_tx_load(dev, data->ctx.tx_buf, spi_cfg,
-							len, last_packet);
+				   len, last_packet, rx_ignore);
 
 	return ret;
 }