[PATCH v4 3/4] mtd: spi-nor: otp: return -EROFS if region is read-only

From: Michael Walle
Date: Fri May 21 2021 - 15:40:53 EST


SPI NOR flashes will just ignore program commands if the OTP region is
locked. Thus, a user might not notice that the intended write didn't end
up in the flash. Return -EROFS to the user in this case. From what I can
tell, chips/cfi_cmdset_0001.c also return this error code.

One could optimize spi_nor_mtd_otp_range_is_locked() to read the status
register only once and not for every OTP region, but for that we would
need some more invasive changes. Given that this is
one-time-programmable memory and the normal access mode is reading, we
just live with the small overhead.

Fixes: 069089acf88b ("mtd: spi-nor: add OTP support")
Signed-off-by: Michael Walle <michael@xxxxxxxx>
---
drivers/mtd/spi-nor/otp.c | 35 +++++++++++++++++++++++++++++++++++
1 file changed, 35 insertions(+)

diff --git a/drivers/mtd/spi-nor/otp.c b/drivers/mtd/spi-nor/otp.c
index 3898ed67ba1c..b87f96593c13 100644
--- a/drivers/mtd/spi-nor/otp.c
+++ b/drivers/mtd/spi-nor/otp.c
@@ -249,6 +249,31 @@ static int spi_nor_mtd_otp_info(struct mtd_info *mtd, size_t len,
return ret;
}

+static int spi_nor_mtd_otp_range_is_locked(struct spi_nor *nor, loff_t ofs,
+ size_t len)
+{
+ const struct spi_nor_otp_ops *ops = nor->params->otp.ops;
+ unsigned int region;
+ int locked;
+
+ if (!len)
+ return 0;
+
+ /*
+ * If any of the affected OTP regions are locked the entire range is
+ * considered locked.
+ */
+ for (region = spi_nor_otp_offset_to_region(nor, ofs);
+ region <= spi_nor_otp_offset_to_region(nor, ofs + len - 1);
+ region++) {
+ locked = ops->is_locked(nor, region);
+ if (locked)
+ return locked;
+ }
+
+ return 0;
+}
+
static int spi_nor_mtd_otp_read_write(struct mtd_info *mtd, loff_t ofs,
size_t total_len, size_t *retlen,
const u8 *buf, bool is_write)
@@ -271,6 +296,16 @@ static int spi_nor_mtd_otp_read_write(struct mtd_info *mtd, loff_t ofs,
/* don't access beyond the end */
total_len = min_t(size_t, total_len, spi_nor_otp_size(nor) - ofs);

+ if (is_write) {
+ ret = spi_nor_mtd_otp_range_is_locked(nor, ofs, total_len);
+ if (ret < 0) {
+ goto out;
+ } else if (ret) {
+ ret = -EROFS;
+ goto out;
+ }
+ }
+
*retlen = 0;
while (total_len) {
/*
--
2.20.1