bootutil: Fix compatible sector checking

Fixes an issue whereby slot sizes were checked but the check was
not done properly. This also adds debug log messages to show the
sector configuration including if slot sizes are not optimal

Signed-off-by: Jamie McCrae <jamie.mccrae@nordicsemi.no>

Author: nordicjm

boot/bootutil/src/swap_move.c

@@ -234,6 +234,28 @@ boot_status_internal_off(const struct boot_status *bs, int elem_sz)
     return off;
 }
 
+static int app_max_sectors(struct boot_loader_state *state)
+{
+    uint32_t sz = 0;
+    uint32_t sector_sz;
+    uint32_t trailer_sz;
+    uint32_t first_trailer_idx;
+
+    sector_sz = boot_img_sector_size(state, BOOT_PRIMARY_SLOT, 0);
+    trailer_sz = boot_trailer_sz(BOOT_WRITE_SZ(state));
+    first_trailer_idx = boot_img_num_sectors(state, BOOT_PRIMARY_SLOT) - 1;
+
+    while (1) {
+        sz += sector_sz;
+        if  (sz >= trailer_sz) {
+            break;
+        }
+        first_trailer_idx--;
+    }
+
+    return first_trailer_idx;
+}
+
 int
 boot_slots_compatible(struct boot_loader_state *state)
 {
@@ -242,20 +264,31 @@ boot_slots_compatible(struct boot_loader_state *state)
     size_t sector_sz_pri = 0;
     size_t sector_sz_sec = 0;
     size_t i;
+    size_t num_usable_sectors_pri;
 
     num_sectors_pri = boot_img_num_sectors(state, BOOT_PRIMARY_SLOT);
     num_sectors_sec = boot_img_num_sectors(state, BOOT_SECONDARY_SLOT);
+    num_usable_sectors_pri = app_max_sectors(state);
+
     if ((num_sectors_pri != num_sectors_sec) &&
-            (num_sectors_pri != (num_sectors_sec + 1))) {
+            (num_sectors_pri != (num_sectors_sec + 1)) &&
+            (num_usable_sectors_pri != (num_sectors_sec + 1))) {
         BOOT_LOG_WRN("Cannot upgrade: not a compatible amount of sectors");
+        BOOT_LOG_DBG("slot0 sectors: %d, slot1 sectors: %d, usable slot0 sectors: %d",
+                     (int)num_sectors_pri, (int)num_sectors_sec,
+                     (int)(num_usable_sectors_pri - 1));
         return 0;
-    }
-
-    if (num_sectors_pri > BOOT_MAX_IMG_SECTORS) {
+    } else if (num_sectors_pri > BOOT_MAX_IMG_SECTORS) {
         BOOT_LOG_WRN("Cannot upgrade: more sectors than allowed");
         return 0;
     }
 
+    if (num_usable_sectors_pri != (num_sectors_sec + 1)) {
+        BOOT_LOG_DBG("Non-optimal sector distribution, slot0 has %d usable sectors (%d assigned) "
+                     "but slot1 has %d assigned", (int)(num_usable_sectors_pri - 1),
+                     (int)num_sectors_pri, (int)num_sectors_sec);
+    }
+
     for (i = 0; i < num_sectors_sec; i++) {
         sector_sz_pri = boot_img_sector_size(state, BOOT_PRIMARY_SLOT, i);
         sector_sz_sec = boot_img_sector_size(state, BOOT_SECONDARY_SLOT, i);
@@ -544,24 +577,11 @@ swap_run(struct boot_loader_state *state, struct boot_status *bs,
 
 int app_max_size(struct boot_loader_state *state)
 {
-    uint32_t sz = 0;
     uint32_t sector_sz;
-    uint32_t trailer_sz;
-    uint32_t first_trailer_idx;
 
     sector_sz = boot_img_sector_size(state, BOOT_PRIMARY_SLOT, 0);
-    trailer_sz = boot_trailer_sz(BOOT_WRITE_SZ(state));
-    first_trailer_idx = boot_img_num_sectors(state, BOOT_PRIMARY_SLOT) - 1;
-
-    while (1) {
-        sz += sector_sz;
-        if  (sz >= trailer_sz) {
-            break;
-        }
-        first_trailer_idx--;
-    }
 
-    return (first_trailer_idx * sector_sz);
+    return (app_max_sectors(state) * sector_sz);
 }
 
 #endif