mtd: spi-nor: core: avoid odd length/address reads on 8D-8D-8D mode

mtd: spi-nor: core: avoid odd length/address reads on 8D-8D-8D mode

[ Upstream commit f156b23df6a84efb2f6686156be94d4988568954 ]

On Octal DTR capable flashes like Micron Xcella reads cannot start or
end at an odd address in Octal DTR mode. Extra bytes need to be read at
the start or end to make sure both the start address and length remain
even.

To avoid allocating too much extra memory, thereby putting unnecessary
memory pressure on the system, the temporary buffer containing the extra
padding bytes is capped at PAGE_SIZE bytes. The rest of the 2-byte
aligned part should be read directly in the main buffer.

Signed-off-by: Pratyush Yadav <p.yadav@ti.com>
Reviewed-by: Michael Walle <michael@walle.cc>
Signed-off-by: Luke Wang <ziniu.wang_1@nxp.com>
Signed-off-by: Pratyush Yadav <pratyush@kernel.org>
Link: https://lore.kernel.org/r/20250708091646.292-1-ziniu.wang_1@nxp.com
[ Resolve conflict in drivers/mtd/spi-nor/core.c.
  In spi_nor_read(), 6.1.y contains a spi_nor_convert_addr() call
  before spi_nor_read_data(), introduced by 364995962803 ("mtd:
  spi-nor: Add a ->convert_addr() method"), which does not exist in
  mainline. This call is specific to Xilinx S3AN flashes, which use a
  non-standard address format. In mainline, S3AN flash support was
  removed entirely, and the corresponding spi_nor_convert_addr() call
  was dropped by 9539d12d9f52 ("mtd: spi-nor: get rid of non-power-of-2
  page size handling"). Keep the existing spi_nor_convert_addr() call
  and insert the new spi_nor_octal_dtr_read() branch after it. ]
Signed-off-by: Liyin Zhang <liyin.zhang.cn@windriver.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>