mtd: spi-nor: make lock/unlock bounds checks more obvious and robust

There are a few different corner cases to the current logic that seem
undesirable:

* mtd_lock() with offs==0 trips a bounds issue on
  ofs - mtd->erasesize < 0

* mtd_unlock() on the middle of a flash that is already unlocked will
  return -EINVAL

* probably other corner cases

So, let's stop doing "smart" checks like "check the block below us",
let's just do the following:

(a) pass only non-negative offsets/lengths to stm_is_locked_sr()
(b) add a similar stm_is_unlocked_sr() function, so we can check if the
    *entire* range is unlocked (and not just whether some part of it is
    unlocked)

Then armed with (b), we can make lock() and unlock() much more
symmetric:

(c) short-circuit the procedure if there is no work to be done, and
(d) check the entire range above/below

This also aligns well with the structure needed for proper TB
(Top/Bottom) support.

Signed-off-by: Brian Norris <computersforpeace@gmail.com>
Tested-by: Ezequiel Garcia <ezequiel@vanguardiasur.com.ar>

diff --git a/drivers/mtd/spi-nor/spi-nor.c b/drivers/mtd/spi-nor/spi-nor.c
index 3dde727..680bc15 100644 (file)
--- a/drivers/mtd/spi-nor/spi-nor.c
+++ b/drivers/mtd/spi-nor/spi-nor.c
@@ -439,17 +439,38 @@ static void stm_get_locked_range(struct spi_nor *nor, u8 sr, loff_t *ofs,
 }
 
 /*
- * Return 1 if the entire region is locked, 0 otherwise
+ * Return 1 if the entire region is locked (if @locked is true) or unlocked (if
+ * @locked is false); 0 otherwise
  */
-static int stm_is_locked_sr(struct spi_nor *nor, loff_t ofs, uint64_t len,
-                           u8 sr)
+static int stm_check_lock_status_sr(struct spi_nor *nor, loff_t ofs, uint64_t len,
+                                   u8 sr, bool locked)
 {
        loff_t lock_offs;
        uint64_t lock_len;
 
+       if (!len)
+               return 1;
+
        stm_get_locked_range(nor, sr, &lock_offs, &lock_len);
 
-       return (ofs + len <= lock_offs + lock_len) && (ofs >= lock_offs);
+       if (locked)
+               /* Requested range is a sub-range of locked range */
+               return (ofs + len <= lock_offs + lock_len) && (ofs >= lock_offs);
+       else
+               /* Requested range does not overlap with locked range */
+               return (ofs >= lock_offs + lock_len) || (ofs + len <= lock_offs);
+}
+
+static int stm_is_locked_sr(struct spi_nor *nor, loff_t ofs, uint64_t len,
+                           u8 sr)
+{
+       return stm_check_lock_status_sr(nor, ofs, len, sr, true);
+}
+
+static int stm_is_unlocked_sr(struct spi_nor *nor, loff_t ofs, uint64_t len,
+                             u8 sr)
+{
+       return stm_check_lock_status_sr(nor, ofs, len, sr, false);
 }
 
 /*
@@ -481,20 +502,24 @@ static int stm_lock(struct spi_nor *nor, loff_t ofs, uint64_t len)
        int status_old, status_new;
        u8 mask = SR_BP2 | SR_BP1 | SR_BP0;
        u8 shift = ffs(mask) - 1, pow, val;
+       loff_t lock_len;
        int ret;
 
        status_old = read_sr(nor);
        if (status_old < 0)
                return status_old;
 
-       /* SPI NOR always locks to the end */
-       if (ofs + len != mtd->size) {
-               /* Does combined region extend to end? */
-               if (!stm_is_locked_sr(nor, ofs + len, mtd->size - ofs - len,
-                                     status_old))
-                       return -EINVAL;
-               len = mtd->size - ofs;
-       }
+       /* If nothing in our range is unlocked, we don't need to do anything */
+       if (stm_is_locked_sr(nor, ofs, len, status_old))
+               return 0;
+
+       /* If anything above us is unlocked, we can't use 'top' protection */
+       if (!stm_is_locked_sr(nor, ofs + len, mtd->size - (ofs + len),
+                               status_old))
+               return -EINVAL;
+
+       /* lock_len: length of region that should end up locked */
+       lock_len = mtd->size - ofs;
 
        /*
         * Need smallest pow such that:
@@ -505,7 +530,7 @@ static int stm_lock(struct spi_nor *nor, loff_t ofs, uint64_t len)
         *
         *   pow = ceil(log2(size / len)) = log2(size) - floor(log2(len))
         */
-       pow = ilog2(mtd->size) - ilog2(len);
+       pow = ilog2(mtd->size) - ilog2(lock_len);
        val = mask - (pow << shift);
        if (val & ~mask)
                return -EINVAL;
@@ -541,17 +566,24 @@ static int stm_unlock(struct spi_nor *nor, loff_t ofs, uint64_t len)
        int status_old, status_new;
        u8 mask = SR_BP2 | SR_BP1 | SR_BP0;
        u8 shift = ffs(mask) - 1, pow, val;
+       loff_t lock_len;
        int ret;
 
        status_old = read_sr(nor);
        if (status_old < 0)
                return status_old;
 
-       /* Cannot unlock; would unlock larger region than requested */
-       if (stm_is_locked_sr(nor, ofs - mtd->erasesize, mtd->erasesize,
-                            status_old))
+       /* If nothing in our range is locked, we don't need to do anything */
+       if (stm_is_unlocked_sr(nor, ofs, len, status_old))
+               return 0;
+
+       /* If anything below us is locked, we can't use 'top' protection */
+       if (!stm_is_unlocked_sr(nor, 0, ofs, status_old))
                return -EINVAL;
 
+       /* lock_len: length of region that should remain locked */
+       lock_len = mtd->size - (ofs + len);
+
        /*
         * Need largest pow such that:
         *
@@ -561,8 +593,8 @@ static int stm_unlock(struct spi_nor *nor, loff_t ofs, uint64_t len)
         *
         *   pow = floor(log2(size / len)) = log2(size) - ceil(log2(len))
         */
-       pow = ilog2(mtd->size) - order_base_2(mtd->size - (ofs + len));
-       if (ofs + len == mtd->size) {
+       pow = ilog2(mtd->size) - order_base_2(lock_len);
+       if (lock_len == 0) {
                val = 0; /* fully unlocked */
        } else {
                val = mask - (pow << shift);