boards: st: nucleo_h753zi: update and reorder flash partitions

- Increase the size of the storage partition to 2 sectors
because a single sector makes it unusable as reported
by test_flash_copy.

This change will breaks backward compatibility regarding
MCUboot firmware update support.

Add a migration guide note about changes to the flash layout
and warn users about potential firmware upgrade failures.

Signed-off-by: Fabrice DJIATSA <[email protected]>

Author: djiatsaf-st

boards/st/nucleo_h753zi/nucleo_h753zi.dts

@@ -248,28 +248,22 @@ zephyr_udc0: &usbotg_fs {
 			read-only;
 		};
 
-		/* storage: 128KB for settings */
-		storage_partition: partition@20000 {
-			label = "storage";
-			reg = <0x00020000 DT_SIZE_K(128)>;
-		};
-
 		/* application image slot: 256KB */
-		slot0_partition: partition@40000 {
+		slot0_partition: partition@20000 {
 			label = "image-0";
-			reg = <0x00040000 DT_SIZE_K(256)>;
+			reg = <0x00020000 DT_SIZE_K(256)>;
 		};
 
 		/* backup slot: 256KB */
-		slot1_partition: partition@80000 {
+		slot1_partition: partition@60000 {
 			label = "image-1";
-			reg = <0x00080000 DT_SIZE_K(256)>;
+			reg = <0x00060000 DT_SIZE_K(256)>;
 		};
 
-		/* swap slot: 128KB */
-		scratch_partition: partition@c0000 {
-			label = "image-scratch";
-			reg = <0x000c0000 DT_SIZE_K(128)>;
+		/* storage: 256KB for settings */
+		storage_partition: partition@a0000 {
+			label = "storage";
+			reg = <0x000a0000 DT_SIZE_K(256)>;
 		};
 	};
 };

doc/releases/migration-guide-4.3.rst

@@ -68,6 +68,10 @@ Boards
   external NOR flash. This change currently prevents upgrade from older Zephyr release images to
   Zephyr 4.3 release images. More details in the TF-M migration and release notes.
 
+* nucleo_h753zi: the flash layout was updated and firmware upgrade may fail due to layout
+  incompatibility with the previous layout. The new layout includes storage partition enlarged to
+  2 sectors, scratch partition removed and all flash partitions reordered for better structure.
+
 * mimxrt11x0: renamed lpadc1 to lpadc2 and renamed lpadc0 to lpadc1.
 
 * NXP ``frdm_mcxa166`` is renamed to ``frdm_mcxa346``.