mtd: nand: allow drivers to request minimum alignment for passed buffer

In some cases, nand_do_{read,write}_ops is passed with unaligned
ops->datbuf.  Drivers using DMA will be unhappy about unaligned
buffer.

The new struct member, buf_align, represents the minimum alignment
the driver require for the buffer.  If the buffer passed from the
upper MTD layer does not have enough alignment, nand_do_*_ops will
use bufpoi.
Signed-off-by: Masahiro Yamada <yamada.masahiro@socionext.com>
Signed-off-by: Boris Brezillon <boris.brezillon@free-electrons.com>

drivers/mtd/nand/nand_base.c

@@ -1954,7 +1954,9 @@ static int nand_do_read_ops(struct mtd_info *mtd, loff_t from,
 		if (!aligned)
 			use_bufpoi = 1;
 		else if (chip->options & NAND_USE_BOUNCE_BUFFER)
-			use_bufpoi = !virt_addr_valid(buf);
+			use_bufpoi = !virt_addr_valid(buf) ||
+				     !IS_ALIGNED((unsigned long)buf,
+						 chip->buf_align);
 		else
 			use_bufpoi = 0;
 
@@ -2810,7 +2812,9 @@ static int nand_do_write_ops(struct mtd_info *mtd, loff_t to,
 		if (part_pagewr)
 			use_bufpoi = 1;
 		else if (chip->options & NAND_USE_BOUNCE_BUFFER)
-			use_bufpoi = !virt_addr_valid(buf);
+			use_bufpoi = !virt_addr_valid(buf) ||
+				     !IS_ALIGNED((unsigned long)buf,
+						 chip->buf_align);
 		else
 			use_bufpoi = 0;
 
@@ -3429,6 +3433,8 @@ static void nand_set_defaults(struct nand_chip *chip)
 		nand_hw_control_init(chip->controller);
 	}
 
+	if (!chip->buf_align)
+		chip->buf_align = 1;
 }
 
 /* Sanitize ONFI strings so we can safely print them */

include/linux/mtd/nand.h

@@ -755,6 +755,7 @@ struct nand_manufacturer_ops {
  *			setting the read-retry mode. Mostly needed for MLC NAND.
  * @ecc:		[BOARDSPECIFIC] ECC control structure
  * @buffers:		buffer structure for read/write
+ * @buf_align:		minimum buffer alignment required by a platform
  * @hwcontrol:		platform-specific hardware control structure
  * @erase:		[REPLACEABLE] erase function
  * @scan_bbt:		[REPLACEABLE] function to scan bad block table
@@ -905,6 +906,7 @@ struct nand_chip {
 
 	struct nand_ecc_ctrl ecc;
 	struct nand_buffers *buffers;
+	unsigned long buf_align;
 	struct nand_hw_control hwcontrol;
 
 	uint8_t *bbt;