For platforms with DT populated, use dma_request_slave_channel()
to acquire the DMA channel. For !DT platforms, we fall back to
explicitly passing the omap_dma_filter_fn() to dma_request_channel().
Once all platforms boot from DT, the dma_request_channel() path can
be dropped.

Signed-off-by: Matt Porter <redacted>
---
 drivers/spi/spi-omap2-mcspi.c |   68 +++++++++++++++++++++++++++++------------
 1 file changed, 48 insertions(+), 20 deletions(-)

diff --git a/drivers/spi/spi-omap2-mcspi.c b/drivers/spi/spi-omap2-mcspi.c
index 9502566..1cf1072 100644
--- a/drivers/spi/spi-omap2-mcspi.c
+++ b/drivers/spi/spi-omap2-mcspi.c

@@ -104,6 +104,9 @@ struct omap2_mcspi_dma {
 
 	struct completion dma_tx_completion;
 	struct completion dma_rx_completion;
+
+	char dma_rx_ch_name[14];
+	char dma_tx_ch_name[14];
 };
 
 /* use PIO for small transfers, avoiding DMA setup/teardown overhead and

@@ -798,14 +801,26 @@ static int omap2_mcspi_request_dma(struct spi_device *spi)
 	dma_cap_zero(mask);
 	dma_cap_set(DMA_SLAVE, mask);
 	sig = mcspi_dma->dma_rx_sync_dev;
-	mcspi_dma->dma_rx = dma_request_channel(mask, omap_dma_filter_fn, &sig);
+	if (spi->dev.of_node)
+		mcspi_dma->dma_rx =
+			dma_request_slave_channel(&master->dev,
+						  mcspi_dma->dma_rx_ch_name);
+	else
+		mcspi_dma->dma_rx =
+			dma_request_channel(mask, omap_dma_filter_fn, &sig);
 	if (!mcspi_dma->dma_rx) {
 		dev_err(&spi->dev, "no RX DMA engine channel for McSPI\n");
 		return -EAGAIN;
 	}