[PATCH v2 3/3] mtd: spi-nor: add locking support for is25xxxxx device

From: Sagar Shrikant Kadam
Date: Sun Apr 28 2019 - 14:10:02 EST


The locking scheme for ISSI devices is based on stm_lock mechanism.
The is25xxxxx devices have 4 bits for selecting the range of blocks to
be locked for write.

The current implementation, blocks entire 512 blocks of flash memory.

Signed-off-by: Sagar Shrikant Kadam <sagar.kadam@xxxxxxxxxx>
---
drivers/mtd/spi-nor/spi-nor.c | 60 +++++++++++++++++++++++++++++++++++++++++++
1 file changed, 60 insertions(+)

diff --git a/drivers/mtd/spi-nor/spi-nor.c b/drivers/mtd/spi-nor/spi-nor.c
index 81c7b3e..2dba7e9 100644
--- a/drivers/mtd/spi-nor/spi-nor.c
+++ b/drivers/mtd/spi-nor/spi-nor.c
@@ -1459,6 +1459,65 @@ static int macronix_quad_enable(struct spi_nor *nor)

return 0;
}
+/**
+ * Lock a region of the flash.Implementation is based on stm_lock
+ * Supports the block protection bits BP{0,1,2,3} in the status register
+ * Returns negative on errors, 0 on success.
+ */
+static int issi_lock(struct spi_nor *nor, loff_t ofs, uint64_t len)
+{
+ struct mtd_info *mtd = &nor->mtd;
+ int status_old, status_new;
+ u8 mask = SR_BP3 | SR_BP2 | SR_BP1 | SR_BP0;
+ u8 shift = ffs(mask) - 1, pow, val = 0;
+ loff_t lock_len;
+ bool use_top = true;
+
+ status_old = read_sr(nor);
+
+ if (status_old < 0)
+ return status_old;
+
+ /* lock_len: length of region that should end up locked */
+ if (use_top)
+ lock_len = mtd->size - ofs;
+ else
+ lock_len = ofs + len;
+
+ /*
+ * Need smallest pow such that:
+ *
+ * 1 / (2^pow) <= (len / size)
+ *
+ * so (assuming power-of-2 size) we do:
+ *
+ * pow = ceil(log2(size / len)) = log2(size) - floor(log2(len))
+ */
+ pow = ilog2(mtd->size) - ilog2(lock_len);
+ val = mask - (pow << shift);
+
+ if (val & ~mask)
+ return -EINVAL;
+
+ /* Don't "lock" with no region! */
+ if (!(val & mask))
+ return -EINVAL;
+
+ status_new = (status_old & ~mask & ~SR_TB) | val;
+
+ /* Disallow further writes if WP pin is asserted */
+ status_new |= SR_SRWD;
+
+ /* Don't bother if they're the same */
+ if (status_new == status_old)
+ return 0;
+
+ /* Only modify protection if it will not unlock other areas */
+ if ((status_new & mask) < (status_old & mask))
+ return -EINVAL;
+
+ return write_sr_and_check(nor, status_new, mask);
+}

/**
* issi_unlock() - clear BP[0123] write-protection.
@@ -4121,6 +4180,7 @@ int spi_nor_scan(struct spi_nor *nor, const char *name,
/* NOR protection support for ISSI chips */
if (JEDEC_MFR(info) == SNOR_MFR_ISSI ||
info->flags & SPI_NOR_HAS_LOCK) {
+ nor->flash_lock = issi_lock;
nor->flash_unlock = issi_unlock;

}
--
1.9.1