[PATCH v3 1/5] mtd: spi-nor: Fix gap in SR block protection locking

[<Tudor.Ambarus@microchip.com>]

From: Tudor Ambarus <tudor.ambarus@microchip.com>

Fix the gap for the SR block protection, the BP bits were set with
a +1 value than actually needed. This patch does not change the
behavior of the locking operations, just fixes the protected areas.

On a 16Mbit flash with 64KByte erase sector, the following changed
for the lock operation:

Number of blocks | BP2:0 before | BP2:0 now |
               1 | 010b         | 001b      |
               2 | 110b         | 010b      |
               3 | 110b         | 010b      |
               4 | 100b         | 011b      |
               5 | 100b         | 011b      |
               6 | 100b         | 011b      |
               7 | 100b         | 011b      |
               8 | 101b         | 100b      |
               9 | 101b         | 100b      |
             ... | ...          | ...       |

For the lock operation, if one requests to lock an area that is not
matching the upper boundary of a BP protected area, we round down
the total length and lock less than the user requested, in order to
not lock more than the user actually requested.

For the unlock operation, read the number of blocks column as
"locked all but number of blocks value". On a 16Mbit flash with
64KByte erase sector, the following changed for the lock operation:

Number of blocks | BP2:0 before | BP2:0 now |
               1 | 111b         | 101b      |
             ... | ...          | ...       |
              15 | 111b         | 101b      |
              16 | 110b         | 101b      |
              17 | 110b         | 100b      |
             ... | ...          | ...       |
              24 | 101b         | 100b      |
              25 | 101b         | 011b      |
              26 | 101b         | 011b      |
              27 | 101b         | 011b      |
              28 | 100b         | 011b      |
              29 | 100b         | 010b      |
              30 | 011b         | 010b      |
              31 | 010b         | 001b      |
              32 | 000b         | 000b      |

For the unlock operation, if one requests to unlock an area that is
not matching the upper boundary of a BP protected area, we round up
the total length and unlock more than the user actually requested.

Signed-off-by: Tudor Ambarus <tudor.ambarus@microchip.com>
---
 drivers/mtd/spi-nor/core.c | 12 ++++++------
 1 file changed, 6 insertions(+), 6 deletions(-)

diff --git a/drivers/mtd/spi-nor/core.c b/drivers/mtd/spi-nor/core.c
index 877557dbda7f..36660068bc04 100644
--- a/drivers/mtd/spi-nor/core.c
+++ b/drivers/mtd/spi-nor/core.c
@@ -1654,13 +1654,13 @@ static int spi_nor_sr_lock(struct spi_nor *nor, loff_t ofs, uint64_t len)
 	/*
 	 * Need smallest pow such that:
 	 *
-	 *   1 / (2^pow) <= (len / size)
+	 *   1 / ((2^pow) - 1) <= (len / size)
 	 *
 	 * so (assuming power-of-2 size) we do:
 	 *
-	 *   pow = ceil(log2(size / len)) = log2(size) - floor(log2(len))
+	 *   pow = ceil(log2(size / len)) = log2(size) - floor(log2(len)) + 1
 	 */
-	pow = ilog2(mtd->size) - ilog2(lock_len);
+	pow = ilog2(mtd->size) - ilog2(lock_len) + 1;
 	val = mask - (pow << SR_BP_SHIFT);
 	if (val & ~mask)
 		return -EINVAL;
@@ -1739,13 +1739,13 @@ static int spi_nor_sr_unlock(struct spi_nor *nor, loff_t ofs, uint64_t len)
 	/*
 	 * Need largest pow such that:
 	 *
-	 *   1 / (2^pow) >= (len / size)
+	 *   1 / ((2^pow) - 1) >= (len / size)
 	 *
 	 * so (assuming power-of-2 size) we do:
 	 *
-	 *   pow = floor(log2(size / len)) = log2(size) - ceil(log2(len))
+	 *   pow = floor(log2(size / len)) = log2(size) - ceil(log2(len)) + 1
 	 */
-	pow = ilog2(mtd->size) - order_base_2(lock_len);
+	pow = ilog2(mtd->size) - order_base_2(lock_len) + 1;
 	if (lock_len == 0) {
 		val = 0; /* fully unlocked */
 	} else {
-- 
2.23.0

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