[PATCH 3/3] mtd: m25p80: add support of SPI 1-2-2 and 1-4-4 protocols

[Cyrille Pitchen]

Before this patch, m25p80_read() supported few SPI protocols:
- regular SPI 1-1-1
- SPI Dual Output 1-1-2
- SPI Quad Output 1-1-4
On the other hand, m25p80_write() only supported SPI 1-1-1.

This patch updates both m25p80_read() and m25p80_write() functions to let
them support SPI 1-2-2 and SPI 1-4-4 protocols for Fast Read and Page
Program SPI commands.

It adopts a conservative approach to avoid regressions. Hence the new
implementations try to be as close as possible to the old implementations,
so the main differences are:
- the tx_nbits values now being set properly for the spi_transfer
  structures carrying the (op code + address/dummy) bytes
- and the spi_transfer structure being split into 2 spi_transfer
  structures when the numbers of I/O lines are different for op code and
  for address/dummy byte transfers on the SPI bus.

Besides, the current spi-nor framework supports neither the SPI 2-2-2 nor
the SPI 4-4-4 protocols. So, for now, we don't need to update the
m25p80_{read|write}_reg() functions as SPI 1-1-1 is the only one possible
protocol.

Signed-off-by: Cyrille Pitchen <cyrille.pitchen@xxxxxxxxx>
---
 drivers/mtd/devices/m25p80.c | 122 ++++++++++++++++++++++++++++++++-----------
 1 file changed, 92 insertions(+), 30 deletions(-)

diff --git a/drivers/mtd/devices/m25p80.c b/drivers/mtd/devices/m25p80.c
index f56b38b1f57b..cdc0a007400a 100644
--- a/drivers/mtd/devices/m25p80.c
+++ b/drivers/mtd/devices/m25p80.c
@@ -34,6 +34,19 @@ struct m25p {
 	u8			command[MAX_CMD_SIZE];
 };
 
+static inline void m25p80_proto2nbits(enum spi_nor_protocol proto,
+				      unsigned int *code_nbits,
+				      unsigned int *addr_nbits,
+				      unsigned int *data_nbits)
+{
+	if (code_nbits)
+		*code_nbits = SNOR_PROTO_CODE_FROM_PROTO(proto);
+	if (addr_nbits)
+		*addr_nbits = SNOR_PROTO_ADDR_FROM_PROTO(proto);
+	if (data_nbits)
+		*data_nbits = SNOR_PROTO_DATA_FROM_PROTO(proto);
+}
+
 static int m25p80_read_reg(struct spi_nor *nor, u8 code, u8 *val, int len)
 {
 	struct m25p *flash = nor->priv;
@@ -78,11 +91,16 @@ static ssize_t m25p80_write(struct spi_nor *nor, loff_t to, size_t len,
 {
 	struct m25p *flash = nor->priv;
 	struct spi_device *spi = flash->spi;
-	struct spi_transfer t[2] = {};
+	unsigned int code_nbits, addr_nbits, data_nbits, data_idx;
+	struct spi_transfer t[3] = {};
 	struct spi_message m;
 	int cmd_sz = m25p_cmdsz(nor);
 	ssize_t ret;
 
+	/* get transfer protocols. */
+	m25p80_proto2nbits(nor->write_proto, &code_nbits,
+			   &addr_nbits, &data_nbits);
+
 	spi_message_init(&m);
 
 	if (nor->program_opcode == SPINOR_OP_AAI_WP && nor->sst_write_second)
@@ -92,12 +110,27 @@ static ssize_t m25p80_write(struct spi_nor *nor, loff_t to, size_t len,
 	m25p_addr2cmd(nor, to, flash->command);
 
 	t[0].tx_buf = flash->command;
+	t[0].tx_nbits = code_nbits;
 	t[0].len = cmd_sz;
 	spi_message_add_tail(&t[0], &m);
 
-	t[1].tx_buf = buf;
-	t[1].len = len;
-	spi_message_add_tail(&t[1], &m);
+	/* split the op code and address bytes into two transfers if needed. */
+	data_idx = 1;
+	if (addr_nbits != code_nbits) {
+		t[0].len = 1;
+
+		t[1].tx_buf = &flash->command[1];
+		t[1].tx_nbits = addr_nbits;
+		t[1].len = cmd_sz - 1;
+		spi_message_add_tail(&t[1], &m);
+
+		data_idx = 2;
+	}
+
+	t[data_idx].tx_buf = buf;
+	t[data_idx].tx_nbits = data_nbits;
+	t[data_idx].len = len;
+	spi_message_add_tail(&t[data_idx], &m);
 
 	ret = spi_sync(spi, &m);
 	if (ret)
@@ -109,18 +142,6 @@ static ssize_t m25p80_write(struct spi_nor *nor, loff_t to, size_t len,
 	return ret;
 }
 
-static inline unsigned int m25p80_rx_nbits(struct spi_nor *nor)
-{
-	switch (nor->read_proto) {
-	case SNOR_PROTO_1_1_2:
-		return 2;
-	case SNOR_PROTO_1_1_4:
-		return 4;
-	default:
-		return 0;
-	}
-}
-
 /*
  * Read an address range from the nor chip.  The address range
  * may be any size provided it is within the physical boundaries.
@@ -130,13 +151,19 @@ static ssize_t m25p80_read(struct spi_nor *nor, loff_t from, size_t len,
 {
 	struct m25p *flash = nor->priv;
 	struct spi_device *spi = flash->spi;
-	struct spi_transfer t[2];
+	unsigned int code_nbits, addr_nbits, data_nbits, data_idx;
+	struct spi_transfer t[3];
 	struct spi_message m;
 	unsigned int dummy = nor->read_dummy;
 	ssize_t ret;
+	int cmd_sz;
+
+	/* get transfer protocols. */
+	m25p80_proto2nbits(nor->read_proto, &code_nbits,
+			   &addr_nbits, &data_nbits);
 
 	/* convert the dummy cycles to the number of bytes */
-	dummy /= 8;
+	dummy = (dummy * addr_nbits) / 8;
 
 	if (spi_flash_read_supported(spi)) {
 		struct spi_flash_read_message msg;
@@ -149,10 +176,9 @@ static ssize_t m25p80_read(struct spi_nor *nor, loff_t from, size_t len,
 		msg.read_opcode = nor->read_opcode;
 		msg.addr_width = nor->addr_width;
 		msg.dummy_bytes = dummy;
-		/* TODO: Support other combinations */
-		msg.opcode_nbits = SPI_NBITS_SINGLE;
-		msg.addr_nbits = SPI_NBITS_SINGLE;
-		msg.data_nbits = m25p80_rx_nbits(nor);
+		msg.opcode_nbits = code_nbits;
+		msg.addr_nbits = addr_nbits;
+		msg.data_nbits = data_nbits;
 
 		ret = spi_flash_read(spi, &msg);
 		if (ret < 0)
@@ -167,20 +193,45 @@ static ssize_t m25p80_read(struct spi_nor *nor, loff_t from, size_t len,
 	m25p_addr2cmd(nor, from, flash->command);
 
 	t[0].tx_buf = flash->command;
+	t[0].tx_nbits = code_nbits;
 	t[0].len = m25p_cmdsz(nor) + dummy;
 	spi_message_add_tail(&t[0], &m);
 
-	t[1].rx_buf = buf;
-	t[1].rx_nbits = m25p80_rx_nbits(nor);
-	t[1].len = min3(len, spi_max_transfer_size(spi),
-			spi_max_message_size(spi) - t[0].len);
-	spi_message_add_tail(&t[1], &m);
+	/*
+	 * Set all dummy/mode cycle bits to avoid sending some manufacturer
+	 * specific pattern, which might make the memory enter its Continuous
+	 * Read mode by mistake.
+	 * Based on the different mode cycle bit patterns listed and described
+	 * in the JESD216B speficication, the 0xff value works for all memories
+	 * and all manufacturers.
+	 */
+	cmd_sz = t[0].len;
+	memset(flash->command + cmd_sz - dummy, 0xff, dummy);
+
+	/* split the op code and address bytes into two transfers if needed. */
+	data_idx = 1;
+	if (addr_nbits != code_nbits) {
+		t[0].len = 1;
+
+		t[1].tx_buf = &flash->command[1];
+		t[1].tx_nbits = addr_nbits;
+		t[1].len = cmd_sz - 1;
+		spi_message_add_tail(&t[1], &m);
+
+		data_idx = 2;
+	}
+
+	t[data_idx].rx_buf = buf;
+	t[data_idx].rx_nbits = data_nbits;
+	t[data_idx].len = min3(len, spi_max_transfer_size(spi),
+			       spi_max_message_size(spi) - cmd_sz);
+	spi_message_add_tail(&t[data_idx], &m);
 
 	ret = spi_sync(spi, &m);
 	if (ret)
 		return ret;
 
-	ret = m.actual_length - m25p_cmdsz(nor) - dummy;
+	ret = m.actual_length - cmd_sz;
 	if (ret < 0)
 		return -EIO;
 	return ret;
@@ -224,11 +275,22 @@ static int m25p_probe(struct spi_device *spi)
 	spi_set_drvdata(spi, flash);
 	flash->spi = spi;
 
-	if (spi->mode & SPI_RX_QUAD)
+	if (spi->mode & SPI_RX_QUAD) {
 		modes.rd_modes |= SNOR_MODE_1_1_4;
-	else if (spi->mode & SPI_RX_DUAL)
+
+		if (spi->mode & SPI_TX_QUAD) {
+			modes.rd_modes |= SNOR_MODE_1_4_4;
+			modes.wr_modes |= (SNOR_MODE_1_1_4 | SNOR_MODE_1_4_4);
+		}
+	} else if (spi->mode & SPI_RX_DUAL) {
 		modes.rd_modes |= SNOR_MODE_1_1_2;
 
+		if (spi->mode & SPI_TX_DUAL) {
+			modes.rd_modes |= SNOR_MODE_1_2_2;
+			modes.wr_modes |= (SNOR_MODE_1_1_2 | SNOR_MODE_1_2_2);
+		}
+	}
+
 	if (data && data->name)
 		nor->mtd.name = data->name;
 
-- 
2.7.4