[PATCH v2] mtd: spi-nor: Do not proceed with spi_nor_sr_unlock if WP

[Matija Glavinic Pecotic]

In case Status register 1:SR_SRWD was set (either by software or write
protect pin), sr_unlock fails on spi_nor_write_sr_and_check in 8-bit
mode due to fact that written value will not match read value.

Problem was observed with n25q128a11 device having protection enabled
by W# pin. Failures lead to device probe failure.

Problem was uncovered by 82de6a6fb67e16 ("mtd: spi-nor: Fix the writing
of the Status Register on micron flashes"). Commit selected 8-bit mode
for micron devices. In 16-bit mode, CR content is verified, while in
8-bit SR is checked for sanity.

Signed-off-by: Matija Glavinic Pecotic <matija.glavinic-pecotic.ext at nokia.com>
---
v2: Fix whitespaces added by mail client

 drivers/mtd/spi-nor/core.c | 4 ++++
 1 file changed, 4 insertions(+)

diff --git a/drivers/mtd/spi-nor/core.c b/drivers/mtd/spi-nor/core.c
index 65eff4c..4c3acc0 100644
--- a/drivers/mtd/spi-nor/core.c
+++ b/drivers/mtd/spi-nor/core.c
@@ -1777,6 +1777,10 @@ static int spi_nor_sr_unlock(struct spi_nor *nor, loff_t ofs, uint64_t len)
 
 	status_old = nor->bouncebuf[0];
 
+	/* If SR is write protected, we cannot unlock */
+	if (status_old & SR_SRWD)
+		return 0;
+
 	/* If nothing in our range is locked, we don't need to do anything */
 	if (spi_nor_is_unlocked_sr(nor, ofs, len, status_old))
 		return 0;
-- 
2.10.2