[PATCH v4] mtd/nand: don't use {read,write}_buf for 8-bit transfers

Uwe Kleine-König
2013-12-05T21:22:38Z

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>
---
Changes since v2, sent with
Message-Id: 1362415655-13073-1-git-send-email-u.kleine-koenig@pengutronix.de:

- use a proper uint16_t instead of a 2 byte array to pass to chip->write_buf
to fix endianess issue. Noticed by David Woodhouse. (This also gets rid of
the Compound Literal that catched David's eye.)

Changes since v3, sent with
Message-id:1385500515-5376-1-git-send-email-u.kleine-koenig@pengutronix.de (v3)

- drop whitespace cleanup
- support resetting to 16 bit width function on 2nd call of nand_set_defaults

drivers/mtd/nand/nand_base.c | 57 ++++++++++++++++++++++++++++++++++++++++++--
include/linux/mtd/nand.h | 3 +++
2 files changed, 58 insertions(+), 2 deletions(-)

diff --git a/drivers/mtd/nand/nand_base.c b/drivers/mtd/nand/nand_base.c
index bd39f7b..3a6e95f 100644
--- a/drivers/mtd/nand/nand_base.c
+++ b/drivers/mtd/nand/nand_base.c
@@ -202,6 +202,51 @@ 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, &word, 2);
+}
+
+/**
* nand_write_buf - [DEFAULT] write buffer to chip
* @mtd: MTD device structure
* @buf: data buffer
@@ -2716,6 +2761,7 @@ 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)
@@ -2723,7 +2769,9 @@ 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;
@@ -2740,6 +2788,8 @@ 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))
@@ -2749,7 +2799,8 @@ 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;
}

@@ -2812,6 +2863,8 @@ 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)
diff --git a/include/linux/mtd/nand.h b/include/linux/mtd/nand.h
index 9e6c8f9..e843942 100644
--- a/include/linux/mtd/nand.h
+++ b/include/linux/mtd/nand.h
@@ -432,6 +432,8 @@ struct nand_buffers {
* flash device.
* @read_byte: [REPLACEABLE] read one byte from the chip
* @read_word: [REPLACEABLE] read one word from the chip
+ * @write_byte [REPLACEABLE] write a single byte to the chip on the
+ * low 8 I/O lines
* @write_buf: [REPLACEABLE] write data from the buffer to the chip
* @read_buf: [REPLACEABLE] read data from the chip into the buffer
* @select_chip: [REPLACEABLE] select chip nr
@@ -521,6 +523,7 @@ struct nand_chip {

uint8_t (*read_byte)(struct mtd_info *mtd);
u16 (*read_word)(struct mtd_info *mtd);
+ void (*write_byte)(struct mtd_info *mtd, uint8_t byte);
void (*write_buf)(struct mtd_info *mtd, const uint8_t *buf, int len);
void (*read_buf)(struct mtd_info *mtd, uint8_t *buf, int len);
void (*select_chip)(struct mtd_info *mtd, int chip);
--
1.8.4.3