[PATCH v8 3/9] mtd: spi-nor: core: Allow specifying the byte order in Octal DTR mode

[Jaime Liao <jaimeliao.tw@gmail.com>]

From: JaimeLiao <jaimeliao@mxic.com.tw>

Macronix swaps bytes on a 16-bit boundary when configured in Octal DTR.
The byte order of 16-bit words is swapped when read or written in 8D-8D-8D
mode compared to STR modes. Allow operations to specify the byte order in
DTR mode, so that controllers can swap the bytes back at run-time to
address the flash's endianness requirements, if they are capable. If the
controllers are not capable of swapping the bytes, the protocol is
downgrade via spi_nor_spimem_adjust_hwcaps(). When available, the swapping
of the bytes is always done regardless if it's a data or register access,
so that we comply with the JESD216 requirements: "Byte order of 16-bit
words is swapped when read in 8D-8D-8D mode compared to 1-1-1".

Merge Tudor's patch and add modifications for suiting newer version
of Linux kernel.

Suggested-by: Michael Walle <mwalle@kernel.org>
Signed-off-by: Tudor Ambarus <tudor.ambarus@linaro.org>
Signed-off-by: JaimeLiao <jaimeliao@mxic.com.tw>
---
 drivers/mtd/spi-nor/core.c | 5 +++++
 drivers/mtd/spi-nor/core.h | 1 +
 2 files changed, 6 insertions(+)

diff --git a/drivers/mtd/spi-nor/core.c b/drivers/mtd/spi-nor/core.c
index 4129764fad8c..0076007e1cde 100644
--- a/drivers/mtd/spi-nor/core.c
+++ b/drivers/mtd/spi-nor/core.c
@@ -113,6 +113,11 @@ void spi_nor_spimem_setup_op(const struct spi_nor *nor,
 		op->cmd.opcode = (op->cmd.opcode << 8) | ext;
 		op->cmd.nbytes = 2;
 	}
+
+	/* SWAP16 is only applicable when Octal DTR mode */
+	if (nor->read_proto == SNOR_PROTO_8_8_8_DTR)
+		if (nor->flags & SNOR_F_SWAP16)
+			op->data.swap16 = true;
 }
 
 /**
diff --git a/drivers/mtd/spi-nor/core.h b/drivers/mtd/spi-nor/core.h
index d36c0e072954..3c5190ac0a79 100644
--- a/drivers/mtd/spi-nor/core.h
+++ b/drivers/mtd/spi-nor/core.h
@@ -140,6 +140,7 @@ enum spi_nor_option_flags {
 	SNOR_F_RWW		= BIT(14),
 	SNOR_F_ECC		= BIT(15),
 	SNOR_F_NO_WP		= BIT(16),
+	SNOR_F_SWAP16		= BIT(17),
 };
 
 struct spi_nor_read_command {
-- 
2.25.1