spi: dw-dma: Detach DMA transfer into a dedicated method

In order to add an alternative method of DMA-based SPI transfer first we
need to detach the currently available one from the common code. Here we
move the normal DMA-based SPI transfer execution functionality into a
dedicated method. It will be utilized if either the DMA engine supports
an unlimited number SG entries or Tx-only SPI transfer is requested. But
currently just use it for any SPI transfer.

Signed-off-by: Serge Semin <Sergey.Semin@baikalelectronics.ru>
Link: https://lore.kernel.org/r/20200920112322.24585-9-Sergey.Semin@baikalelectronics.ru
Signed-off-by: Mark Brown <broonie@kernel.org>

drivers/spi/spi-dw-dma.c

@@ -441,7 +441,8 @@ static int dw_spi_dma_setup(struct dw_spi *dws, struct spi_transfer *xfer)
 	return 0;
 }
 
-static int dw_spi_dma_transfer(struct dw_spi *dws, struct spi_transfer *xfer)
+static int dw_spi_dma_transfer_all(struct dw_spi *dws,
+				   struct spi_transfer *xfer)
 {
 	int ret;
 
@@ -462,7 +463,14 @@ static int dw_spi_dma_transfer(struct dw_spi *dws, struct spi_transfer *xfer)
 
 	dma_async_issue_pending(dws->txchan);
 
-	ret = dw_spi_dma_wait(dws, xfer);
+	return dw_spi_dma_wait(dws, xfer);
+}
+
+static int dw_spi_dma_transfer(struct dw_spi *dws, struct spi_transfer *xfer)
+{
+	int ret;
+
+	ret = dw_spi_dma_transfer_all(dws, xfer);
 	if (ret)
 		return ret;