can: mcp251x: remove custom DMA mapped buffer

There is no need to duplicate what SPI core already does, i.e. mapping buffers
for DMA capable transfers. This patch removes all related pices of code.
Tested-by: NSean Nyekjaer <sean@geanix.com>
Signed-off-by: NMarc Kleine-Budde <mkl@pengutronix.de>

drivers/net/can/spi/mcp251x.c

@@ -47,7 +47,6 @@
 #include <linux/completion.h>
 #include <linux/delay.h>
 #include <linux/device.h>
-#include <linux/dma-mapping.h>
 #include <linux/freezer.h>
 #include <linux/interrupt.h>
 #include <linux/io.h>
@@ -202,10 +201,6 @@
 
 #define DEVICE_NAME "mcp251x"
 
-static int mcp251x_enable_dma; /* Enable SPI DMA. Default: 0 (Off) */
-module_param(mcp251x_enable_dma, int, 0444);
-MODULE_PARM_DESC(mcp251x_enable_dma, "Enable SPI DMA. Default: 0 (Off)");
-
 static const struct can_bittiming_const mcp251x_bittiming_const = {
 	.name = DEVICE_NAME,
 	.tseg1_min = 3,
@@ -234,8 +229,6 @@ struct mcp251x_priv {
 
 	u8 *spi_tx_buf;
 	u8 *spi_rx_buf;
-	dma_addr_t spi_tx_dma;
-	dma_addr_t spi_rx_dma;
 
 	struct sk_buff *tx_skb;
 	int tx_len;
@@ -304,13 +297,6 @@ static int mcp251x_spi_trans(struct spi_device *spi, int len)
 	int ret;
 
 	spi_message_init(&m);
-
-	if (mcp251x_enable_dma) {
-		t.tx_dma = priv->spi_tx_dma;
-		t.rx_dma = priv->spi_rx_dma;
-		m.is_dma_mapped = 1;
-	}
-
 	spi_message_add_tail(&t, &m);
 
 	ret = spi_sync(spi, &m);
@@ -1097,42 +1083,18 @@ static int mcp251x_can_probe(struct spi_device *spi)
 	priv->spi = spi;
 	mutex_init(&priv->mcp_lock);
 
-	/* If requested, allocate DMA buffers */
-	if (mcp251x_enable_dma) {
-		spi->dev.coherent_dma_mask = ~0;
-
-		/* Minimum coherent DMA allocation is PAGE_SIZE, so allocate
-		 * that much and share it between Tx and Rx DMA buffers.
-		 */
-		priv->spi_tx_buf = dmam_alloc_coherent(&spi->dev,
-						       PAGE_SIZE,
-						       &priv->spi_tx_dma,
-						       GFP_DMA);
-
-		if (priv->spi_tx_buf) {
-			priv->spi_rx_buf = (priv->spi_tx_buf + (PAGE_SIZE / 2));
-			priv->spi_rx_dma = (dma_addr_t)(priv->spi_tx_dma +
-							(PAGE_SIZE / 2));
-		} else {
-			/* Fall back to non-DMA */
-			mcp251x_enable_dma = 0;
-		}
+	priv->spi_tx_buf = devm_kzalloc(&spi->dev, SPI_TRANSFER_BUF_LEN,
+					GFP_KERNEL);
+	if (!priv->spi_tx_buf) {
+		ret = -ENOMEM;
+		goto error_probe;
 	}
 
-	/* Allocate non-DMA buffers */
-	if (!mcp251x_enable_dma) {
-		priv->spi_tx_buf = devm_kzalloc(&spi->dev, SPI_TRANSFER_BUF_LEN,
-						GFP_KERNEL);
-		if (!priv->spi_tx_buf) {
-			ret = -ENOMEM;
-			goto error_probe;
-		}
-		priv->spi_rx_buf = devm_kzalloc(&spi->dev, SPI_TRANSFER_BUF_LEN,
-						GFP_KERNEL);
-		if (!priv->spi_rx_buf) {
-			ret = -ENOMEM;
-			goto error_probe;
-		}
+	priv->spi_rx_buf = devm_kzalloc(&spi->dev, SPI_TRANSFER_BUF_LEN,
+					GFP_KERNEL);
+	if (!priv->spi_rx_buf) {
+		ret = -ENOMEM;
+		goto error_probe;
 	}
 
 	SET_NETDEV_DEV(net, &spi->dev);