[PATCH 1/1] spi-nor: always respect write-protect input

[Jonas Bonn]

The status register bit SRWD (status register write disable) is
described in many words in the datasheets but effectively boils down to:

i) if set, respect WP# when trying to change protection bits;
ii) if unset, ignore WP# when trying to change protection bits

In short, the bit determines whether the WP# signal is honored or not.

It's difficult to imagine the use-case where the WP# is connected and
asserted but the user doesn't want to respect its setting.  As such,
this patch sets the SRWD bit unconditionally so that the WP# is _always_
respected; hardware that doesn't care about WP# normally won't even have
it connected.

Tested on a Cypress s25fl512s.  With this patch, the WP# is always
respected, irregardless of whether any flash protection bits are set.

Signed-off-by: Jonas Bonn <jonas@xxxxxxxxxxx>
CC: Marek Vasut <marek.vasut@xxxxxxxxx>
CC: David Woodhouse <dwmw2@xxxxxxxxxxxxx>
CC: Brian Norris <computersforpeace@xxxxxxxxx>
CC: Boris Brezillon <bbrezillon@xxxxxxxxxx>
CC: Richard Weinberger <richard@xxxxxx>
CC: linux-mtd@xxxxxxxxxxxxxxxxxxx
---
 drivers/mtd/spi-nor/spi-nor.c | 18 +++++++++++-------
 1 file changed, 11 insertions(+), 7 deletions(-)

diff --git a/drivers/mtd/spi-nor/spi-nor.c b/drivers/mtd/spi-nor/spi-nor.c
index c6064479b614..c960c097e0bc 100644
--- a/drivers/mtd/spi-nor/spi-nor.c
+++ b/drivers/mtd/spi-nor/spi-nor.c
@@ -1230,9 +1230,6 @@ static int stm_lock(struct spi_nor *nor, loff_t ofs, uint64_t len)
 
 	status_new = (status_old & ~mask & ~SR_TB) | val;
 
-	/* Disallow further writes if WP pin is asserted */
-	status_new |= SR_SRWD;
-
 	if (!use_top)
 		status_new |= SR_TB;
 
@@ -1312,10 +1309,6 @@ static int stm_unlock(struct spi_nor *nor, loff_t ofs, uint64_t len)
 
 	status_new = (status_old & ~mask & ~SR_TB) | val;
 
-	/* Don't protect status register if we're fully unlocked */
-	if (lock_len == 0)
-		status_new &= ~SR_SRWD;
-
 	if (!use_top)
 		status_new |= SR_TB;
 
@@ -3918,6 +3911,7 @@ static int spi_nor_setup(struct spi_nor *nor,
 static int spi_nor_init(struct spi_nor *nor)
 {
 	int err;
+	int sr;
 
 	/*
 	 * Atmel, SST, Intel/Numonyx, and others serial NOR tend to power up
@@ -3953,6 +3947,16 @@ static int spi_nor_init(struct spi_nor *nor)
 		set_4byte(nor, true);
 	}
 
+	/* Always respect the WP# (write-protect) input */
+	sr = read_sr(nor);
+	if (sr < 0) {
+		dev_err(nor->dev, "error while reading status register\n");
+		return -EINVAL;
+	}
+	sr |= SR_SRWD;
+	return write_sr_and_check(nor, sr, SR_SRWD);
+
+
 	return 0;
 }
 
-- 
2.19.1