dmaengine: mxs: Add header file to be shared with gpmi nand driver

The mxs dma driver can do PIO transfers. A pointer to the PIO words
to transfer is passed in the struct scatterlist * argument of
dmaengine_prep_slave_sg(). It's quite ugly and non obvious to cast
u32 * to struct scatterlist * each time when calling
dmaengine_prep_slave_sg(), so add a static inline wrapper function
to be called by the user along with a description what is going on.

Signed-off-by: Sascha Hauer <s.hauer@pengutronix.de>
Acked-by: Vinod Koul <vkoul@kernel.org>
Signed-off-by: Miquel Raynal <miquel.raynal@bootlin.com>

drivers/dma/mxs-dma.c

@@ -24,6 +24,7 @@
 #include <linux/of_device.h>
 #include <linux/of_dma.h>
 #include <linux/list.h>
+#include <linux/dma/mxs-dma.h>
 
 #include <asm/irq.h>
 

drivers/mtd/nand/raw/gpmi-nand/gpmi-nand.c

@@ -15,6 +15,7 @@
 #include <linux/of.h>
 #include <linux/of_device.h>
 #include <linux/pm_runtime.h>
+#include <linux/dma/mxs-dma.h>
 #include "gpmi-nand.h"
 #include "gpmi-regs.h"
 #include "bch-regs.h"
@@ -914,9 +915,8 @@ static int gpmi_send_command(struct gpmi_nand_data *this)
 		| BM_GPMI_CTRL0_ADDRESS_INCREMENT
 		| BF_GPMI_CTRL0_XFER_COUNT(this->command_length);
 	pio[1] = pio[2] = 0;
-	desc = dmaengine_prep_slave_sg(channel,
-					(struct scatterlist *)pio,
-					ARRAY_SIZE(pio), DMA_TRANS_NONE, 0);
+	desc = mxs_dmaengine_prep_pio(channel, pio, ARRAY_SIZE(pio),
+				      DMA_TRANS_NONE, 0);
 	if (!desc)
 		return -EINVAL;
 
@@ -988,8 +988,8 @@ static int gpmi_send_data(struct gpmi_nand_data *this, const void *buf, int len)
 		| BF_GPMI_CTRL0_ADDRESS(address)
 		| BF_GPMI_CTRL0_XFER_COUNT(len);
 	pio[1] = 0;
-	desc = dmaengine_prep_slave_sg(channel, (struct scatterlist *)pio,
-					ARRAY_SIZE(pio), DMA_TRANS_NONE, 0);
+	desc = mxs_dmaengine_prep_pio(channel, pio, ARRAY_SIZE(pio),
+				      DMA_TRANS_NONE, 0);
 	if (!desc)
 		return -EINVAL;
 
@@ -1025,9 +1025,8 @@ static int gpmi_read_data(struct gpmi_nand_data *this, void *buf, int len)
 		| BF_GPMI_CTRL0_ADDRESS(BV_GPMI_CTRL0_ADDRESS__NAND_DATA)
 		| BF_GPMI_CTRL0_XFER_COUNT(len);
 	pio[1] = 0;
-	desc = dmaengine_prep_slave_sg(channel,
-					(struct scatterlist *)pio,
-					ARRAY_SIZE(pio), DMA_TRANS_NONE, 0);
+	desc = mxs_dmaengine_prep_pio(channel, pio, ARRAY_SIZE(pio),
+				      DMA_TRANS_NONE, 0);
 	if (!desc)
 		return -EINVAL;
 
@@ -1083,10 +1082,8 @@ static int gpmi_send_page(struct gpmi_nand_data *this, dma_addr_t payload,
 	pio[4] = payload;
 	pio[5] = auxiliary;
 
-	desc = dmaengine_prep_slave_sg(channel,
-					(struct scatterlist *)pio,
-					ARRAY_SIZE(pio), DMA_TRANS_NONE,
-					DMA_CTRL_ACK);
+	desc = mxs_dmaengine_prep_pio(channel, pio, ARRAY_SIZE(pio),
+				      DMA_TRANS_NONE, DMA_CTRL_ACK);
 	if (!desc)
 		return -EINVAL;
 
@@ -1117,9 +1114,7 @@ static int gpmi_read_page(struct gpmi_nand_data *this, dma_addr_t payload,
 		| BF_GPMI_CTRL0_ADDRESS(address)
 		| BF_GPMI_CTRL0_XFER_COUNT(0);
 	pio[1] = 0;
-	desc = dmaengine_prep_slave_sg(channel,
-				(struct scatterlist *)pio, 2,
-				DMA_TRANS_NONE, 0);
+	desc = mxs_dmaengine_prep_pio(channel, pio, 2, DMA_TRANS_NONE, 0);
 	if (!desc)
 		return -EINVAL;
 
@@ -1144,10 +1139,8 @@ static int gpmi_read_page(struct gpmi_nand_data *this, dma_addr_t payload,
 	pio[3] = geo->page_size;
 	pio[4] = payload;
 	pio[5] = auxiliary;
-	desc = dmaengine_prep_slave_sg(channel,
-					(struct scatterlist *)pio,
-					ARRAY_SIZE(pio), DMA_TRANS_NONE,
-					DMA_CTRL_ACK);
+	desc = mxs_dmaengine_prep_pio(channel, pio, ARRAY_SIZE(pio),
+				      DMA_TRANS_NONE, DMA_CTRL_ACK);
 	if (!desc)
 		return -EINVAL;
 
@@ -1163,9 +1156,8 @@ static int gpmi_read_page(struct gpmi_nand_data *this, dma_addr_t payload,
 		| BF_GPMI_CTRL0_XFER_COUNT(geo->page_size);
 	pio[1] = 0;
 	pio[2] = 0; /* clear GPMI_HW_GPMI_ECCCTRL, disable the BCH. */
-	desc = dmaengine_prep_slave_sg(channel,
-				(struct scatterlist *)pio, 3,
-				DMA_TRANS_NONE, DMA_CTRL_ACK);
+	desc = mxs_dmaengine_prep_pio(channel, pio, 3, DMA_TRANS_NONE,
+				      DMA_CTRL_ACK);
 	if (!desc)
 		return -EINVAL;
 

include/linux/dma/mxs-dma.h

@@ -0,0 +1,21 @@
+/* SPDX-License-Identifier: GPL-2.0 */
+#ifndef _MXS_DMA_H_
+#define _MXS_DMA_H_
+
+#include <linux/dmaengine.h>
+
+/*
+ * The mxs dmaengine can do PIO transfers. We pass a pointer to the PIO words
+ * in the second argument to dmaengine_prep_slave_sg when the direction is
+ * set to DMA_TRANS_NONE. To make this clear and to prevent users from doing
+ * the error prone casting we have this wrapper function
+ */
+static inline struct dma_async_tx_descriptor *mxs_dmaengine_prep_pio(
+        struct dma_chan *chan, u32 *pio, unsigned int npio,
+        enum dma_transfer_direction dir, unsigned long flags)
+{
+	return dmaengine_prep_slave_sg(chan, (struct scatterlist *)pio, npio,
+				       dir, flags);
+}
+
+#endif /* _MXS_DMA_H_ */