boards: st: n6: avoid access to last 32B of memory-mapped XSPI device

System might become unstable when the last 32 bytes of a XSPI attached
are accessed in memory-mapped mode with cache enabled.
In order to prevent this, remove the last 32-bytes of the PSRAM on the
stm32n6570_dk as well as NOR on the nucleo n657x0_q.
Partitions should also be defined in a way to avoid accessing to the
last 32-bytes of the device.

Issue is described in the STM32N6xxxx errata sheet ES0620 Rev 1:
2.4.5 Deadlock or data corruption when DQS is enabled and the wrap
request includes the last address of the memory

Signed-off-by: Alain Volmat <[email protected]>

Author: Alain Volmat

boards/st/nucleo_n657x0_q/nucleo_n657x0_q_common.dtsi

@@ -246,7 +246,13 @@ zephyr_udc0: &usbotg_hs1 {
 
 			storage_partition: partition@3ff0000 {
 				label = "storage";
-				reg = <0x3ff0000 DT_SIZE_K(64)>;
+				/*
+				 * Prevent access to the last 32bytes of the memory-mapped device
+				 * Issue described in the STM32N6xxxx errata sheet ES0620 Rev 1:
+				 * 2.4.5 Deadlock or data corruption when DQS is enabled and the
+				 * wrap request includes the last address of the memory
+				 */
+				reg = <0x3ff0000 (DT_SIZE_K(64) - 32)>;
 			};
 		};
 	};

boards/st/stm32n6570_dk/stm32n6570_dk_common.dtsi

@@ -41,7 +41,13 @@
 
 	psram: memory@90000000 {
 		compatible = "zephyr,memory-region";
-		reg = <0x90000000 DT_SIZE_M(32)>;
+		/*
+		 * Prevent access to the last 32bytes of the memory-mapped device
+		 * Issue described in the STM32N6xxxx errata sheet ES0620 Rev 1:
+		 * 2.4.5 Deadlock or data corruption when DQS is enabled and the
+		 * wrap request includes the last address of the memory
+		 */
+		reg = <0x90000000 (DT_SIZE_M(32) - 32)>;
 		zephyr,memory-region = "PSRAM";
 		zephyr,memory-attr = <DT_MEM_ARM(ATTR_MPU_RAM_NOCACHE)>;
 	};