mtd: rawnand: Handle the double bytes in NV-DDR mode

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As explained in chapter "NV-DDR / NV-DDR2 / NV-DDR3 and Repeat Bytes" of
the ONFI specification, with some commands (mainly the commands which do
not transfer actual data) the data bytes are repeated twice and it is
the responsibility of the receiver to discard them properly. The
concerned commands are: SET_FEATURES, READ_ID, GET_FEATURES,
READ_STATUS, READ_STATUS_ENHANCED, ODT_CONFIGURE. Hence, in the NAND
core we are only impacted by the implementation of READ_ID, GET_FEATURES
and READ_STATUS.

The logic is the same for all:
2/ Check if it is relevant to read all data bytes twice.
1/ Allocate a buffer with twice the requested size (may be done
   statically).
2/ Update the instruction structure to read these extra bytes in the
   allocated buffer.
3/ Copy the even bytes into the original buffer. The performance hit is
   negligible on such small data transfers anyway and we don't really
   care about performances at this stage anyway.
4/ Free the allocated buffer, if any.

Note: nand_data_read_op() is also impacted because it is theoretically
possible to run the command/address cycles first, and, as another
operation, do the data transfers. In this case we can easily identify
the impacted commands because the force_8bit flag will be set (due to
the same reason: their data does not go through the same pipeline).

Signed-off-by: Miquel Raynal <miquel.raynal@bootlin.com>
Link: https://lore.kernel.org/linux-mtd/20210505213750.257417-15-miquel.raynal@bootlin.com

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Miquel Raynal 2021-05-05 23:37:42 +02:00

parent d7a773e881

commit 09cdb237c3

1 changed files with 85 additions and 8 deletions

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drivers/mtd/nand/raw/nand_base.c

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