drivers: spi: siwx91x: Fix compatibility with gpdma

Because of limitation of gpdma, DMA Rx won't run if user doesn't specify
destination buffer.

Thus, the DMA Rx may stop before the end of the full transaction. So, wait
on DMA Tx instead.

Then, the SPI data won't be consumed by the DMA. We need to properly reset
the fifo before to start a new transaction (it is better to ensure we start
with a clean state before every transaction).

Signed-off-by: Jérôme Pouiller <[email protected]>

Author: jerome-pouiller

drivers/spi/spi_silabs_siwx91x_gspi.c

@@ -192,7 +192,7 @@ static int gspi_siwx91x_config(const struct device *dev, const struct spi_config
 }
 
 #ifdef CONFIG_SPI_SILABS_SIWX91X_GSPI_DMA
-static void gspi_siwx91x_dma_rx_callback(const struct device *dev, void *user_data,
+static void gspi_siwx91x_dma_tx_callback(const struct device *dev, void *user_data,
 					 uint32_t channel, int status)
 {
 	const struct device *spi_dev = (const struct device *)user_data;
@@ -230,7 +230,7 @@ static int gspi_siwx91x_dma_config(const struct device *dev,
 		.block_count = block_count,
 		.head_block = channel->dma_descriptors,
 		.dma_slot = channel->dma_slot,
-		.dma_callback = !is_tx ? &gspi_siwx91x_dma_rx_callback : NULL,
+		.dma_callback = is_tx ? &gspi_siwx91x_dma_tx_callback : NULL,
 		.user_data = (void *)dev,
 	};
 
@@ -411,7 +411,8 @@ static int gspi_siwx91x_transceive_dma(const struct device *dev, const struct sp
 		return -EINVAL;
 	}
 
-	/* Reset the Rx and Tx FIFO register */
+	cfg->reg->GSPI_FIFO_THRLD_b.RFIFO_RESET = 1;
+	cfg->reg->GSPI_FIFO_THRLD_b.WFIFO_RESET = 1;
 	cfg->reg->GSPI_FIFO_THRLD = 0;
 
 	ret = gspi_siwx91x_prepare_dma_transaction(dev, padded_transaction_size);