[PATCH] mtd: spi-nor: fix page offset/remains calculation in spi_nor_write

[Bastian Krause <bst@pengutronix.de>]

nor->write() simply adds the number of written bytes to the pointer
given. Thus retval is incremented in each loop cycle for each
spi_nor_write() call without ever resetting it. This leads to wrong page
offset/remains calculations and an incorrect number of bytes written to
retlen.

This becomes apparant only if the calling function actually compares len
and retlen (e.g. mtd_peb_write() ). Otherwise wrong data is written:

  $ memcpy -s /dev/prng -d prng_data 0 0 10k
  $ erase /dev/mtd0.mypart
  $ cp prng_data /dev/mtd0.mypart
  $ memcmp -s prng_data -d /dev/mtd0.mypart 0 0

memcmp returned "files differ" before, with this patch it returns "OK".

Fixes: c8516869c4 ("spi: Extend the core to ease integration of SPI memory controllers")
Signed-off-by: Bastian Krause <bst@pengutronix.de>
---
 drivers/mtd/spi-nor/spi-nor.c | 1 +
 1 file changed, 1 insertion(+)

diff --git a/drivers/mtd/spi-nor/spi-nor.c b/drivers/mtd/spi-nor/spi-nor.c
index b2052ce0af..9dbc8302ed 100644
--- a/drivers/mtd/spi-nor/spi-nor.c
+++ b/drivers/mtd/spi-nor/spi-nor.c
@@ -972,6 +972,7 @@ static int spi_nor_write(struct mtd_info *mtd, loff_t to, size_t len,
 
 	for (i = 0; i < len; ) {
 		ssize_t written;
+		retval = 0;
 
 		page_offset = (to + i) & (nor->page_size - 1);
 		page_remain = min_t(size_t, nor->page_size - page_offset,
-- 
2.20.1


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