devicetree: Add DT_MEM_FROM_FIXED_PARTITION macro

This is a new fixed-partitions API, which serves as a companion to the
existing `DT_MTD_FROM_FIXED_PARTITION()`. In the following example:

  flash-controller@0 {
          compatible = "flash-controller";
          flash@1000000 {
                  compatible = "soc-nv-flash";
                  partitions {
                          compatible = "fixed-partitions";
                          partition@3a000 {};
                  };
          };
  };

`DT_MTD_FROM_FIXED_PARTITION()` would let us map `partition@3a000` to
`flash-controller@0`. Now, the new `DT_MEM_FROM_FIXED_PARTITION()` can
let us retrieve the memory node (`flash@1000000`) as well, in a manner
consistent with the existing API.

Caution: if a fixed partition is not said to belong to a memory node,
like in this alternative example:

  flash@0 {
          compatible = "spi-nor";
          partitions {
                  compatible = "fixed-partitions";
                  partition@0 {};
          };
  };

then `DT_MEM_FROM_FIXED_PARTITION()` will map `partition@0` to an
invalid node identifier. This partition belongs to `flash@0`, which
could be an MTD on a SPI bus.

For consistency, the existing `DT_MTD_FROM_FIXED_PARTITION()` is now re-
expressed in terms of the new `DT_MEM_FROM_FIXED_PARTITION()`.

Signed-off-by: Grzegorz Swiderski <[email protected]>

Author: 57300

include/zephyr/devicetree/fixed-partitions.h

@@ -78,15 +78,24 @@ extern "C" {
 #define DT_FIXED_PARTITION_ID(node_id) DT_CAT(node_id, _PARTITION_ID)
 
 /**
- * @brief Get the node identifier of the flash device for a partition
+ * @brief Get the node identifier of the flash memory for a partition
+ * @param node_id node identifier for a fixed-partitions child node
+ * @return the node identifier of the internal memory that contains the
+ * fixed-partitions node, or @ref DT_INVALID_NODE if it doesn't exist.
+ */
+#define DT_MEM_FROM_FIXED_PARTITION(node_id)                                                       \
+	COND_CODE_1(DT_NODE_HAS_COMPAT(DT_GPARENT(node_id), soc_nv_flash), (DT_GPARENT(node_id)),  \
+		    (DT_INVALID_NODE))
+
+/**
+ * @brief Get the node identifier of the flash controller for a partition
  * @param node_id node identifier for a fixed-partitions child node
  * @return the node identifier of the memory technology device that
  * contains the fixed-partitions node.
  */
-#define DT_MTD_FROM_FIXED_PARTITION(node_id)				\
-	COND_CODE_1(DT_NODE_HAS_COMPAT(DT_GPARENT(node_id), soc_nv_flash), \
-		    (DT_PARENT(DT_GPARENT(node_id))),			\
-		    (DT_GPARENT(node_id)))
+#define DT_MTD_FROM_FIXED_PARTITION(node_id)                                                       \
+	COND_CODE_1(DT_NODE_EXISTS(DT_MEM_FROM_FIXED_PARTITION(node_id)),                          \
+		    (DT_PARENT(DT_MEM_FROM_FIXED_PARTITION(node_id))), (DT_GPARENT(node_id)))
 
 /**
  * @}