dm: core: Add ofnode to represent device tree nodes

With live tree we need a struct device_node * to reference a node. With
the existing flat tree, we need an int offset. We need to unify these into
a single value which can represent both.

Add an ofnode union for this and adjust existing code to move to this.

Signed-off-by: Simon Glass <sjg@chromium.org>

1 files changed, 96 insertions, 0 deletions

diff --git a/include/dm/ofnode.h b/include/dm/ofnode.h
new file mode 100644
index 0000000000..ed362e134e
--- /dev/null
+++ b/include/dm/ofnode.h
@@ -0,0 +1,96 @@
+/*
+ * Copyright (c) 2017 Google, Inc
+ * Written by Simon Glass <sjg@chromium.org>
+ *
+ * SPDX-License-Identifier:	GPL-2.0+
+ */
+
+#ifndef _DM_OFNODE_H
+#define _DM_OFNODE_H
+
+/**
+ * ofnode - reference to a device tree node
+ *
+ * This union can hold either a straightforward pointer to a struct device_node
+ * in the live device tree, or an offset within the flat device tree. In the
+ * latter case, the pointer value is just the integer offset within the flat DT.
+ *
+ * Thus we can reference nodes in both the live tree (once available) and the
+ * flat tree (until then). Functions are available to translate between an
+ * ofnode and either an offset or a struct device_node *.
+ *
+ * The reference can also hold a null offset, in which case the pointer value
+ * here is (void *)-1. This corresponds to a struct device_node * value of
+ * NULL, or an offset of -1.
+ *
+ * There is no ambiguity as to whether ofnode holds an offset or a node
+ * pointer: when the live tree is active it holds a node pointer, otherwise it
+ * holds an offset. The value itself does not need to be unique and in theory
+ * the same value could point to a valid device node or a valid offset. We
+ * could arrange for a unique value to be used (e.g. by making the pointer
+ * point to an offset within the flat device tree in the case of an offset) but
+ * this increases code size slightly due to the subtraction. Since it offers no
+ * real benefit, the approach described here seems best.
+ *
+ * For now these points use constant types, since we don't allow writing
+ * the DT.
+ *
+ * @np: Pointer to device node, used for live tree
+ * @flat_ptr: Pointer into flat device tree, used for flat tree. Note that this
+ *	is not a really a pointer to a node: it is an offset value. See above.
+ */
+typedef union ofnode_union {
+	const struct device_node *np;	/* will be used for future live tree */
+	long of_offset;
+} ofnode;
+
+/**
+ * ofnode_to_offset() - convert an ofnode to a flat DT offset
+ *
+ * This cannot be called if the reference contains a node pointer.
+ *
+ * @node: Reference containing offset (possibly invalid)
+ * @return DT offset (can be -1)
+ */
+static inline int ofnode_to_offset(ofnode node)
+{
+	return node.of_offset;
+}
+
+/**
+ * ofnode_valid() - check if an ofnode is valid
+ *
+ * @return true if the reference contains a valid ofnode, false if it is NULL
+ */
+static inline bool ofnode_valid(ofnode node)
+{
+	return node.of_offset != -1;
+}
+
+/**
+ * offset_to_ofnode() - convert a DT offset to an ofnode
+ *
+ * @of_offset: DT offset (either valid, or -1)
+ * @return reference to the associated DT offset
+ */
+static inline ofnode offset_to_ofnode(int of_offset)
+{
+	ofnode node;
+
+	node.of_offset = of_offset;
+
+	return node;
+}
+
+/**
+ * ofnode_equal() - check if two references are equal
+ *
+ * @return true if equal, else false
+ */
+static inline bool ofnode_equal(ofnode ref1, ofnode ref2)
+{
+	/* We only need to compare the contents */
+	return ref1.of_offset == ref2.of_offset;
+}
+
+#endif