boards : rpi_pico : Add persistent partition for Pico and Pico_w

Add a 16 KB 'storage' partition at the end of the Pico flash.
That size is sufficient to hold the two test files created by
the 'littlefs' sample.

The sample 'subsys/USB/mass' uses an overlay to add the same
partition and it was changed to delete the one defined by this
DTSI file before doing that.

Signed-off-by: Andreas Wolf <awolf002@gmail.com>

Author: Snap-A

boards/raspberrypi/rpi_pico/rpi_pico-common.dtsi

@@ -62,8 +62,11 @@
 	};
 };
 
+#define FLASH_SIZE		DT_SIZE_M(2)
+#define STORAGE_PARTITION_SIZE	DT_SIZE_K(16)
+
 &flash0 {
-	reg = <0x10000000 DT_SIZE_M(2)>;
+	reg = <0x10000000 FLASH_SIZE>;
 
 	partitions {
 		compatible = "fixed-partitions";
@@ -78,14 +81,25 @@
 		};
 
 		/*
-		 * Usable flash. Starts at 0x100, after the bootloader. The partition
-		 * size is 2MB minus the 0x100 bytes taken by the bootloader.
+		 * Usable flash. Starts at 0x100, after the bootloader. The code partition
+		 * size is flash size minus the 0x100 bytes taken by the bootloader, and
+		 * minus the size of the storage partition.
 		 */
 		code_partition: partition@100 {
 			label = "code-partition";
-			reg = <0x100 (DT_SIZE_M(2) - 0x100)>;
+			reg = <0x100 (FLASH_SIZE - 0x100 - STORAGE_PARTITION_SIZE)>;
 			read-only;
 		};
+
+		/*
+		 * Area for placing a file system for persistent storage. Starts at the end
+		 * of the code partition. The persistent storage size is chosen to have the
+		 * capacity for a minimal 'littlefs' file system with 4 blocks.
+		 */
+		storage_partition: partition@1fc000 {
+			label = "storage-partition";
+			reg = <0x1fc000 STORAGE_PARTITION_SIZE>;
+		};
 	};
 };
 

samples/subsys/usb/mass/boards/rpi_pico.overlay

@@ -5,6 +5,7 @@
  */
 
 /delete-node/ &code_partition;
+/delete-node/ &storage_partition;
 
 &flash0 {
 	partitions {