mtd: nand: don't use {read,write}_buf for 8-bit transfers

According to the Open NAND Flash Interface Specification (ONFI) Revision
3.1 "Parameters are always transferred on the lower 8-bits of the data
bus." for the Get Features and Set Features commands.

So using read_buf and write_buf is wrong for 16-bit wide nand chips as
they use I/O[15:0]. The Get Features command is easily fixed using 4
times the read_byte callback. For Set Features implement a new
overwritable callback "write_byte". Still I expect the default to work
just fine for all controllers and making it overwriteable was just done
for symmetry.

Signed-off-by: Uwe Kleine-König <u.kleine-koenig@pengutronix.de>
[Brian: fixed warning]
Tested-by: Brian Norris <computersforpeace@gmail.com>
Signed-off-by: Brian Norris <computersforpeace@gmail.com>

1 files changed, 55 insertions, 2 deletions

diff --git a/drivers/mtd/nand/nand_base.c b/drivers/mtd/nand/nand_base.c
index b8c74cda7625..d388c7f6fec9 100644
--- a/drivers/mtd/nand/nand_base.c
+++ b/drivers/mtd/nand/nand_base.c
@@ -204,6 +204,51 @@ static void nand_select_chip(struct mtd_info *mtd, int chipnr)
 }
 
 /**
+ * nand_write_byte - [DEFAULT] write single byte to chip
+ * @mtd: MTD device structure
+ * @byte: value to write
+ *
+ * Default function to write a byte to I/O[7:0]
+ */
+static void nand_write_byte(struct mtd_info *mtd, uint8_t byte)
+{
+        struct nand_chip *chip = mtd->priv;
+
+        chip->write_buf(mtd, &byte, 1);
+}
+
+/**
+ * nand_write_byte16 - [DEFAULT] write single byte to a chip with width 16
+ * @mtd: MTD device structure
+ * @byte: value to write
+ *
+ * Default function to write a byte to I/O[7:0] on a 16-bit wide chip.
+ */
+static void nand_write_byte16(struct mtd_info *mtd, uint8_t byte)
+{
+        struct nand_chip *chip = mtd->priv;
+        uint16_t word = byte;
+
+        /*
+         * It's not entirely clear what should happen to I/O[15:8] when writing
+         * a byte. The ONFi spec (Revision 3.1; 2012-09-19, Section 2.16) reads:
+         *
+         *    When the host supports a 16-bit bus width, only data is
+         *    transferred at the 16-bit width. All address and command line
+         *    transfers shall use only the lower 8-bits of the data bus. During
+         *    command transfers, the host may place any value on the upper
+         *    8-bits of the data bus. During address transfers, the host shall
+         *    set the upper 8-bits of the data bus to 00h.
+         *
+         * One user of the write_byte callback is nand_onfi_set_features. The
+         * four parameters are specified to be written to I/O[7:0], but this is
+         * neither an address nor a command transfer. Let's assume a 0 on the
+         * upper I/O lines is OK.
+         */
+        chip->write_buf(mtd, (uint8_t *)&word, 2);
+}
+
+/**
  * nand_write_buf - [DEFAULT] write buffer to chip
  * @mtd: MTD device structure
  * @buf: data buffer
@@ -2769,6 +2814,7 @@ static int nand_onfi_set_features(struct mtd_info *mtd, struct nand_chip *chip,
                         int addr, uint8_t *subfeature_param)
 {
         int status;
+        int i;
 
         if (!chip->onfi_version ||
             !(le16_to_cpu(chip->onfi_params.opt_cmd)
@@ -2776,7 +2822,9 @@ static int nand_onfi_set_features(struct mtd_info *mtd, struct nand_chip *chip,
                 return -EINVAL;
 
         chip->cmdfunc(mtd, NAND_CMD_SET_FEATURES, addr, -1);
-        chip->write_buf(mtd, subfeature_param, ONFI_SUBFEATURE_PARAM_LEN);
+        for (i = 0; i < ONFI_SUBFEATURE_PARAM_LEN; ++i)
+                chip->write_byte(mtd, subfeature_param[i]);
+
         status = chip->waitfunc(mtd, chip);
         if (status & NAND_STATUS_FAIL)
                 return -EIO;
@@ -2793,6 +2841,8 @@ static int nand_onfi_set_features(struct mtd_info *mtd, struct nand_chip *chip,
 static int nand_onfi_get_features(struct mtd_info *mtd, struct nand_chip *chip,
                         int addr, uint8_t *subfeature_param)
 {
+        int i;
+
         if (!chip->onfi_version ||
             !(le16_to_cpu(chip->onfi_params.opt_cmd)
               & ONFI_OPT_CMD_SET_GET_FEATURES))
@@ -2802,7 +2852,8 @@ static int nand_onfi_get_features(struct mtd_info *mtd, struct nand_chip *chip,
         memset(subfeature_param, 0, ONFI_SUBFEATURE_PARAM_LEN);
 
         chip->cmdfunc(mtd, NAND_CMD_GET_FEATURES, addr, -1);
-        chip->read_buf(mtd, subfeature_param, ONFI_SUBFEATURE_PARAM_LEN);
+        for (i = 0; i < ONFI_SUBFEATURE_PARAM_LEN; ++i)
+                *subfeature_param++ = chip->read_byte(mtd);
         return 0;
 }
 
@@ -2865,6 +2916,8 @@ static void nand_set_defaults(struct nand_chip *chip, int busw)
                 chip->block_markbad = nand_default_block_markbad;
         if (!chip->write_buf || chip->write_buf == nand_write_buf)
                 chip->write_buf = busw ? nand_write_buf16 : nand_write_buf;
+        if (!chip->write_byte || chip->write_byte == nand_write_byte)
+                chip->write_byte = busw ? nand_write_byte16 : nand_write_byte;
         if (!chip->read_buf || chip->read_buf == nand_read_buf)
                 chip->read_buf = busw ? nand_read_buf16 : nand_read_buf;
         if (!chip->scan_bbt)