libfdt: Add overlay application function

The device tree overlays are a good way to deal with user-modifyable
boards or boards with some kind of an expansion mechanism where we can
easily plug new board in (like the BBB, the Raspberry Pi or the CHIP).

Add a new function to merge overlays with a base device tree.

Signed-off-by: Maxime Ripard <maxime.ripard@free-electrons.com>

include/libfdt.h

@@ -1740,6 +1740,36 @@ int fdt_add_subnode(void *fdt, int parentoffset, const char *name);
  */
 int fdt_del_node(void *fdt, int nodeoffset);
 
+/**
+ * fdt_overlay_apply - Applies a DT overlay on a base DT
+ * @fdt: pointer to the base device tree blob
+ * @fdto: pointer to the device tree overlay blob
+ *
+ * fdt_overlay_apply() will apply the given device tree overlay on the
+ * given base device tree.
+ *
+ * Expect the base device tree to be modified, even if the function
+ * returns an error.
+ *
+ * returns:
+ *	0, on success
+ *	-FDT_ERR_NOSPACE, there's not enough space in the base device tree
+ *	-FDT_ERR_NOTFOUND, the overlay points to some inexistant nodes or
+ *		properties in the base DT
+ *	-FDT_ERR_BADPHANDLE, the phandles in the overlay do not have the right
+ *		magic
+ *	-FDT_ERR_INTERNAL,
+ *	-FDT_ERR_BADLAYOUT,
+ *	-FDT_ERR_BADMAGIC,
+ *	-FDT_ERR_BADOFFSET,
+ *	-FDT_ERR_BADPATH,
+ *	-FDT_ERR_BADVERSION,
+ *	-FDT_ERR_BADSTRUCTURE,
+ *	-FDT_ERR_BADSTATE,
+ *	-FDT_ERR_TRUNCATED, standard meanings
+ */
+int fdt_overlay_apply(void *fdt, void *fdto);
+
 /**********************************************************************/
 /* Debugging / informational functions                                */
 /**********************************************************************/

lib/Kconfig

@@ -139,6 +139,11 @@ config OF_LIBFDT
 	  particular compatible nodes. The library operates on a flattened
 	  version of the device tree.
 
+config OF_LIBFDT_OVERLAY
+	bool "Enable the FDT library overlay support"
+	help
+	  This enables the FDT library (libfdt) overlay support.
+
 config SPL_OF_LIBFDT
 	bool "Enable the FDT library for SPL"
 	default y if SPL_OF_CONTROL

lib/libfdt/Makefile

@@ -15,3 +15,5 @@ obj-y += \
 	fdt_empty_tree.o \
 	fdt_addresses.o \
 	fdt_region.o
+
+obj-$(CONFIG_OF_LIBFDT_OVERLAY) += fdt_overlay.o

lib/libfdt/fdt_overlay.c

@@ -0,0 +1,405 @@
+#include "libfdt_env.h"
+
+#include <fdt.h>
+#include <libfdt.h>
+
+#include "libfdt_internal.h"
+
+static uint32_t overlay_get_target_phandle(const void *fdto, int fragment)
+{
+	const uint32_t *val;
+	int len;
+
+	val = fdt_getprop(fdto, fragment, "target", &len);
+	if (!val)
+		return 0;
+
+	if ((*val == 0xffffffff) || (len != sizeof(*val)))
+		return 0xffffffff;
+
+	return fdt32_to_cpu(*val);
+}
+
+static int overlay_get_target(const void *fdt, const void *fdto,
+			      int fragment)
+{
+	uint32_t phandle;
+	const char *path;
+
+	/* Try first to do a phandle based lookup */
+	phandle = overlay_get_target_phandle(fdto, fragment);
+	if (phandle == -1)
+		return -FDT_ERR_BADPHANDLE;
+
+	if (phandle)
+		return fdt_node_offset_by_phandle(fdt, phandle);
+
+	/* And then a path based lookup */
+	path = fdt_getprop(fdto, fragment, "target-path", NULL);
+	if (!path)
+		return -FDT_ERR_NOTFOUND;
+
+	return fdt_path_offset(fdt, path);
+}
+
+static int overlay_phandle_add_offset(void *fdt, int node,
+				      const char *name, uint32_t delta)
+{
+	const uint32_t *val;
+	uint32_t adj_val;
+	int len;
+
+	val = fdt_getprop(fdt, node, name, &len);
+	if (!val)
+		return len;
+
+	if (len != sizeof(*val))
+		return -FDT_ERR_BADSTRUCTURE;
+
+	adj_val = fdt32_to_cpu(*val);
+	if ((adj_val + delta) < adj_val)
+		return -FDT_ERR_BADPHANDLE;
+
+	adj_val += delta;
+	return fdt_setprop_inplace_u32(fdt, node, name, adj_val);
+}
+
+static int overlay_adjust_node_phandles(void *fdto, int node,
+					uint32_t delta)
+{
+	bool found = false;
+	int child;
+	int ret;
+
+	ret = overlay_phandle_add_offset(fdto, node, "phandle", delta);
+	if (ret && ret != -FDT_ERR_NOTFOUND)
+		return ret;
+
+	if (!ret)
+		found = true;
+
+	ret = overlay_phandle_add_offset(fdto, node, "linux,phandle", delta);
+	if (ret && ret != -FDT_ERR_NOTFOUND)
+		return ret;
+
+	/*
+	 * If neither phandle nor linux,phandle have been found return
+	 * an error.
+	 */
+	if (!found && !ret)
+		return ret;
+
+	fdt_for_each_subnode(fdto, child, node)
+		overlay_adjust_node_phandles(fdto, child, delta);
+
+	return 0;
+}
+
+static int overlay_adjust_local_phandles(void *fdto, uint32_t delta)
+{
+	/*
+	 * Start adjusting the phandles from the overlay root
+	 */
+	return overlay_adjust_node_phandles(fdto, 0, delta);
+}
+
+static int overlay_update_local_node_references(void *fdto,
+						int tree_node,
+						int fixup_node,
+						uint32_t delta)
+{
+	int fixup_prop;
+	int fixup_child;
+	int ret;
+
+	fdt_for_each_property_offset(fixup_prop, fdto, fixup_node) {
+		const uint32_t *val = NULL;
+		uint32_t adj_val, index;
+		const char *name;
+		int fixup_len;
+		int tree_len;
+
+		val = fdt_getprop_by_offset(fdto, fixup_prop,
+					    &name, &fixup_len);
+		if (!val)
+			return fixup_len;
+		index = fdt32_to_cpu(*val);
+
+		val = fdt_getprop(fdto, tree_node, name, &tree_len);
+		if (!val)
+			return tree_len;
+
+		/*
+		 * The index can be unaligned.
+		 *
+		 * Use a memcpy for the architectures that do not
+		 * support unaligned accesses.
+		 */
+		memcpy(&adj_val, (unsigned char *)val + index,
+		       sizeof(uint32_t));
+
+		adj_val = fdt32_to_cpu(adj_val);
+		adj_val += delta;
+		adj_val = cpu_to_fdt32(adj_val);
+
+		ret = fdt_setprop_inplace_namelen_by_index(fdto, tree_node,
+							   name, strlen(name),
+							   index, &adj_val,
+							   sizeof(adj_val));
+		if (ret)
+			return ret;
+	}
+
+	fdt_for_each_subnode(fdto, fixup_child, fixup_node) {
+		const char *fixup_child_name = fdt_get_name(fdto, fixup_child,
+							    NULL);
+		int tree_child;
+
+		tree_child = fdt_subnode_offset(fdto, tree_node,
+						fixup_child_name);
+		if (tree_child < 0)
+			return tree_child;
+
+		ret = overlay_update_local_node_references(fdto,
+							   tree_child,
+							   fixup_child,
+							   delta);
+		if (ret)
+			return ret;
+	}
+
+	return 0;
+}
+
+static int overlay_update_local_references(void *dto, uint32_t delta)
+{
+	int fixups;
+
+	fixups = fdt_path_offset(dto, "/__local_fixups__");
+	if (fixups < 0) {
+		/* There's no local phandles to adjust, bail out */
+		if (fixups == -FDT_ERR_NOTFOUND)
+			return 0;
+
+		return fixups;
+	}
+
+	/*
+	 * Update our local references from the root of the tree
+	 */
+	return overlay_update_local_node_references(dto, 0, fixups,
+						    delta);
+}
+
+static int overlay_fixup_one_phandle(void *fdt, void *fdto,
+				     int symbols_off,
+				     const char *path, uint32_t path_len,
+				     const char *name, uint32_t name_len,
+				     int index, const char *label)
+{
+	const char *symbol_path;
+	uint32_t phandle;
+	int symbol_off, fixup_off;
+	int prop_len;
+
+	symbol_path = fdt_getprop(fdt, symbols_off, label,
+				  &prop_len);
+	if (!symbol_path)
+		return -FDT_ERR_NOTFOUND;
+
+	symbol_off = fdt_path_offset(fdt, symbol_path);
+	if (symbol_off < 0)
+		return symbol_off;
+
+	phandle = fdt_get_phandle(fdt, symbol_off);
+	if (!phandle)
+		return -FDT_ERR_NOTFOUND;
+
+	fixup_off = fdt_path_offset_namelen(fdto, path, path_len);
+	if (fixup_off < 0)
+		return fixup_off;
+
+	phandle = cpu_to_fdt32(phandle);
+	return fdt_setprop_inplace_namelen_by_index(fdto, fixup_off,
+						    name, name_len, index,
+						    &phandle, sizeof(phandle));
+};
+
+static int overlay_fixup_phandle(void *fdt, void *fdto, int symbols_off,
+				 int property)
+{
+	const char *value;
+	const char *label;
+	int len;
+
+	value = fdt_getprop_by_offset(fdto, property,
+				      &label, &len);
+	if (!value)
+		return len;
+
+	do {
+		const char *prop_string = value;
+		const char *path, *name;
+		uint32_t prop_len = strlen(value);
+		uint32_t path_len, name_len;
+		char *sep, *endptr;
+		int index;
+		int ret;
+
+		path = prop_string;
+		sep = memchr(prop_string, ':', prop_len);
+		if (*sep != ':')
+			return -FDT_ERR_BADSTRUCTURE;
+		path_len = sep - path;
+
+		name = sep + 1;
+		sep = memchr(name, ':', prop_len);
+		if (*sep != ':')
+			return -FDT_ERR_BADSTRUCTURE;
+		name_len = sep - name;
+
+		index = strtoul(sep + 1, &endptr, 10);
+		if ((*endptr != '\0') || (endptr <= (sep + 1)))
+			return -FDT_ERR_BADSTRUCTURE;
+
+		len -= prop_len + 1;
+		value += prop_len + 1;
+
+		ret = overlay_fixup_one_phandle(fdt, fdto, symbols_off,
+						path, path_len, name, name_len,
+						index, label);
+		if (ret)
+			return ret;
+	} while (len > 0);
+
+	return 0;
+}
+
+static int overlay_fixup_phandles(void *dt, void *dto)
+{
+	int fixups_off, symbols_off;
+	int property;
+
+	symbols_off = fdt_path_offset(dt, "/__symbols__");
+	fixups_off = fdt_path_offset(dto, "/__fixups__");
+
+	fdt_for_each_property_offset(property, dto, fixups_off)
+		overlay_fixup_phandle(dt, dto, symbols_off, property);
+
+	return 0;
+}
+
+static int apply_overlay_node(void *dt, int target,
+			      void *dto, int fragment)
+{
+	int property;
+	int node;
+
+	fdt_for_each_property_offset(property, dto, fragment) {
+		const char *name;
+		const void *prop;
+		int prop_len;
+		int ret;
+
+		prop = fdt_getprop_by_offset(dto, property, &name,
+					     &prop_len);
+		if (prop_len == -FDT_ERR_NOTFOUND)
+			return -FDT_ERR_INTERNAL;
+		if (prop_len < 0)
+			return prop_len;
+
+		ret = fdt_setprop(dt, target, name, prop, prop_len);
+		if (ret)
+			return ret;
+	}
+
+	fdt_for_each_subnode(dto, node, fragment) {
+		const char *name = fdt_get_name(dto, node, NULL);
+		int nnode;
+		int ret;
+
+		nnode = fdt_add_subnode(dt, target, name);
+		if (nnode == -FDT_ERR_EXISTS)
+			nnode = fdt_subnode_offset(dt, target, name);
+
+		if (nnode < 0)
+			return nnode;
+
+		ret = apply_overlay_node(dt, nnode, dto, node);
+		if (ret)
+			return ret;
+	}
+
+	return 0;
+}
+
+static int overlay_merge(void *dt, void *dto)
+{
+	int fragment;
+
+	fdt_for_each_subnode(dto, fragment, 0) {
+		int overlay;
+		int target;
+		int ret;
+
+		target = overlay_get_target(dt, dto, fragment);
+		if (target < 0)
+			continue;
+
+		overlay = fdt_subnode_offset(dto, fragment, "__overlay__");
+		if (overlay < 0)
+			return overlay;
+
+		ret = apply_overlay_node(dt, target, dto, overlay);
+		if (ret)
+			return ret;
+	}
+
+	return 0;
+}
+
+int fdt_overlay_apply(void *fdt, void *fdto)
+{
+	uint32_t delta = fdt_get_max_phandle(fdt) + 1;
+	int ret;
+
+	FDT_CHECK_HEADER(fdt);
+	FDT_CHECK_HEADER(fdto);
+
+	ret = overlay_adjust_local_phandles(fdto, delta);
+	if (ret)
+		goto err;
+
+	ret = overlay_update_local_references(fdto, delta);
+	if (ret)
+		goto err;
+
+	ret = overlay_fixup_phandles(fdt, fdto);
+	if (ret)
+		goto err;
+
+	ret = overlay_merge(fdt, fdto);
+	if (ret)
+		goto err;
+
+	/*
+	 * The overlay has been damaged, erase its magic.
+	 */
+	fdt_set_magic(fdto, ~0);
+
+	return 0;
+
+err:
+	/*
+	 * The overlay might have been damaged, erase its magic.
+	 */
+	fdt_set_magic(fdto, ~0);
+
+	/*
+	 * The base device tree might have been damaged, erase its
+	 * magic.
+	 */
+	fdt_set_magic(fdt, ~0);
+
+	return ret;
+}