File 0031-OF-Introduce-DT-overlay-support.patch of Package kernel-adaptation-bbb-v3.12

From 7acfe8a499180a3d6b4d5a9aa791a91933ae7137 Mon Sep 17 00:00:00 2001
From: Pantelis Antoniou <panto@antoniou-consulting.com>
Date: Thu, 3 Jan 2013 12:23:07 +0200
Subject: [PATCH 31/96] OF: Introduce DT overlay support.

Introduce DT overlay support.
Using this functionality it is possible to dynamically overlay a part of
the kernel's tree with another tree that's been dynamically loaded.
It is also possible to remove node and properties.

Note that the I2C client devices are 'special', as in they're not platform
devices. They need to be registered with an I2C specific method.

In general I2C is just no good platform device citizen and needs
special casing.

Signed-off-by: Pantelis Antoniou <panto@antoniou-consulting.com>
---
 Documentation/devicetree/overlay-notes.txt | 179 ++++++
 drivers/of/Kconfig                         |  10 +
 drivers/of/Makefile                        |   1 +
 drivers/of/overlay.c                       | 869 +++++++++++++++++++++++++++++
 include/linux/of.h                         | 113 ++++
 5 files changed, 1172 insertions(+)
 create mode 100644 Documentation/devicetree/overlay-notes.txt
 create mode 100644 drivers/of/overlay.c

diff --git a/Documentation/devicetree/overlay-notes.txt b/Documentation/devicetree/overlay-notes.txt
new file mode 100644
index 0000000..6b43a28e
--- /dev/null
+++ b/Documentation/devicetree/overlay-notes.txt
@@ -0,0 +1,179 @@
+Device Tree Overlay Notes
+-------------------------
+
+This document describes the implementation of the in-kernel
+device tree overlay functionality residing in drivers/of/overlay.c and is a
+companion document to Documentation/devicetree/dt-object-internal.txt[1] &
+Documentation/devicetree/dynamic-resolution-notes.txt[2]
+
+How overlays work
+-----------------
+
+A Device Tree's overlay purpose is to modify the kernel's live tree, and
+have the modification affecting the state of the the kernel in a way that
+is reflecting the changes.
+Since the kernel mainly deals with devices, any new device node that result
+in an active device should have it created while if the device node is either
+disabled or removed all together, the affected device should be deregistered.
+
+Lets take an example where we have a foo board with the following base tree
+which is taken from [1].
+
+---- foo.dts -----------------------------------------------------------------
+	/* FOO platform */
+	/ {
+		compatible = "corp,foo";
+
+		/* shared resources */
+		res: res {
+		};
+
+		/* On chip peripherals */
+		ocp: ocp {
+			/* peripherals that are always instantiated */
+			peripheral1 { ... };
+		}
+	};
+---- foo.dts -----------------------------------------------------------------
+
+The overlay bar.dts, when loaded (and resolved as described in [2]) should
+
+---- bar.dts -----------------------------------------------------------------
+/plugin/;	/* allow undefined label references and record them */
+/ {
+	....	/* various properties for loader use; i.e. part id etc. */
+	fragment@0 {
+		target = <&ocp>;
+		__overlay__ {
+			/* bar peripheral */
+			bar {
+				compatible = "corp,bar";
+				... /* various properties and child nodes */
+			}
+		};
+	};
+};
+---- bar.dts -----------------------------------------------------------------
+
+result in foo+bar.dts
+
+---- foo+bar.dts -------------------------------------------------------------
+	/* FOO platform + bar peripheral */
+	/ {
+		compatible = "corp,foo";
+
+		/* shared resources */
+		res: res {
+		};
+
+		/* On chip peripherals */
+		ocp: ocp {
+			/* peripherals that are always instantiated */
+			peripheral1 { ... };
+
+			/* bar peripheral */
+			bar {
+				compatible = "corp,bar";
+				... /* various properties and child nodes */
+			}
+		}
+	};
+---- foo+bar.dts -------------------------------------------------------------
+
+As a result of the the overlay, a new device node (bar) has been created
+so a bar platform device will be registered and if a matching device driver
+is loaded the device will be created as expected.
+
+Overlay in-kernel API
+---------------------
+
+The steps typically required to get an overlay to work are as follows:
+
+1. Use of_build_overlay_info() to create an array of initialized and
+ready to use of_overlay_info structures.
+2. Call of_overlay() to apply the overlays declared in the array.
+3. If the overlay needs to be removed, call of_overlay_revert().
+4. Finally release the memory taken by the overlay info array by
+of_free_overlay_info().
+
+/**
+ * of_build_overlay_info	- Build an overlay info array
+ * @tree:	Device node containing all the overlays
+ * @cntp:	Pointer to where the overlay info count will be help
+ * @ovinfop:	Pointer to the pointer of an overlay info structure.
+ *
+ * Helper function that given a tree containing overlay information,
+ * allocates and builds an overlay info array containing it, ready
+ * for use using of_overlay.
+ *
+ * Returns 0 on success with the @cntp @ovinfop pointers valid,
+ * while on error a negative error value is returned.
+ */
+int of_build_overlay_info(struct device_node *tree,
+		int *cntp, struct of_overlay_info **ovinfop);
+
+/**
+ * of_free_overlay_info	- Free an overlay info array
+ * @count:	Number of of_overlay_info's
+ * @ovinfo_tab:	Array of overlay_info's to free
+ *
+ * Releases the memory of a previously allocate ovinfo array
+ * by of_build_overlay_info.
+ * Returns 0, or an error if the arguments are bogus.
+ */
+int of_free_overlay_info(int count, struct of_overlay_info *ovinfo_tab);
+
+/**
+ * of_overlay	- Apply @count overlays pointed at by @ovinfo_tab
+ * @count:	Number of of_overlay_info's
+ * @ovinfo_tab:	Array of overlay_info's to apply
+ *
+ * Applies the overlays given, while handling all error conditions
+ * appropriately. Either the operation succeeds, or if it fails the
+ * live tree is reverted to the state before the attempt.
+ * Returns 0, or an error if the overlay attempt failed.
+ */
+int of_overlay(int count, struct of_overlay_info *ovinfo_tab);
+
+/**
+ * of_overlay_revert	- Revert a previously applied overlay
+ * @count:	Number of of_overlay_info's
+ * @ovinfo_tab:	Array of overlay_info's to apply
+ *
+ * Revert a previous overlay. The state of the live tree
+ * is reverted to the one before the overlay.
+ * Returns 0, or an error if the overlay table is not given.
+ */
+int of_overlay_revert(int count, struct of_overlay_info *ovinfo_tab);
+
+Overlay DTS Format
+------------------
+
+The DTS of an overlay should have the following format:
+
+{
+	/* ignored properties by the overlay */
+
+	fragment@0 {	/* first child node */
+		target=<phandle>;	/* target of the overlay */
+		__overlay__ {
+			property-a;	/* add property-a to the target */
+			-property-b;	/* remove property-b from target */
+			node-a {	/* add to an existing, or create a node-a */
+				...
+			};
+			-node-b {	/* remove an existing node-b */
+				...
+			};
+		};
+	}
+	fragment@1 {	/* second child node */
+		...
+	};
+	/* more fragments follow */
+}
+
+It should be noted that the DT overlay format described is the one expected
+by the of_build_overlay_info() function, which is a helper function. There
+is nothing stopping someone coming up with his own DTS format and that will
+end up filling in the fields of the of_overlay_info array.
diff --git a/drivers/of/Kconfig b/drivers/of/Kconfig
index 2a00ae5..c2d5596 100644
--- a/drivers/of/Kconfig
+++ b/drivers/of/Kconfig
@@ -83,4 +83,14 @@ config OF_RESOLVE
 	  Enable OF dynamic resolution support. This allows you to
 	  load Device Tree object fragments are run time.
 
+config OF_OVERLAY
+	bool "OF overlay support"
+	depends on OF
+	select OF_DYNAMIC
+	select OF_DEVICE
+	select OF_RESOLVE
+	help
+	  OpenFirmware overlay support. Allows you to modify on runtime the
+	  live tree using overlays.
+
 endmenu # OF
diff --git a/drivers/of/Makefile b/drivers/of/Makefile
index 93da457..ca466e4 100644
--- a/drivers/of/Makefile
+++ b/drivers/of/Makefile
@@ -10,3 +10,4 @@ obj-$(CONFIG_OF_PCI)	+= of_pci.o
 obj-$(CONFIG_OF_PCI_IRQ)  += of_pci_irq.o
 obj-$(CONFIG_OF_MTD)	+= of_mtd.o
 obj-$(CONFIG_OF_RESOLVE)  += resolver.o
+obj-$(CONFIG_OF_OVERLAY) += overlay.o
diff --git a/drivers/of/overlay.c b/drivers/of/overlay.c
new file mode 100644
index 0000000..61bcfcc
--- /dev/null
+++ b/drivers/of/overlay.c
@@ -0,0 +1,869 @@
+/*
+ * Functions for working with device tree overlays
+ *
+ * Copyright (C) 2012 Pantelis Antoniou <panto@antoniou-consulting.com>
+ * Copyright (C) 2012 Texas Instruments Inc.
+ *
+ * This program is free software; you can redistribute it and/or
+ * modify it under the terms of the GNU General Public License
+ * version 2 as published by the Free Software Foundation.
+ */
+#undef DEBUG
+#include <linux/kernel.h>
+#include <linux/module.h>
+#include <linux/of.h>
+#include <linux/of_device.h>
+#include <linux/i2c.h>
+#include <linux/i2c.h>
+#include <linux/string.h>
+#include <linux/ctype.h>
+#include <linux/errno.h>
+#include <linux/string.h>
+#include <linux/slab.h>
+#include <linux/err.h>
+
+/**
+ * Apply a single overlay node recursively.
+ *
+ * Property or node names that start with '-' signal that
+ * the property/node is to be removed.
+ *
+ * All the property notifiers are appropriately called.
+ * Note that the in case of an error the target node is left
+ * in a inconsistent state. Error recovery should be performed
+ * by recording the modification using the of notifiers.
+ */
+static int of_overlay_apply_one(struct device_node *target,
+		const struct device_node *overlay)
+{
+	const char *pname, *cname;
+	struct device_node *child, *tchild;
+	struct property *prop, *propn, *tprop;
+	int remove;
+	char *full_name;
+	const char *suffix;
+	int ret;
+
+	/* sanity checks */
+	if (target == NULL || overlay == NULL)
+		return -EINVAL;
+
+	for_each_property_of_node(overlay, prop) {
+
+		/* don't touch, 'name' */
+		if (of_prop_cmp(prop->name, "name") == 0)
+			continue;
+
+		/* default is add */
+		remove = 0;
+		pname = prop->name;
+		if (*pname == '-') {	/* skip, - notes removal */
+			pname++;
+			remove = 1;
+			propn = NULL;
+		} else {
+			propn = __of_copy_property(prop,
+					GFP_KERNEL);
+			if (propn == NULL)
+				return -ENOMEM;
+		}
+
+		tprop = of_find_property(target, pname, NULL);
+
+		/* found? */
+		if (tprop != NULL) {
+			if (propn != NULL)
+				ret = of_update_property(target, propn);
+			else
+				ret = of_remove_property(target, tprop);
+		} else {
+			if (propn != NULL)
+				ret = of_add_property(target, propn);
+			else
+				ret = 0;
+		}
+		if (ret != 0)
+			return ret;
+	}
+
+	__for_each_child_of_node(overlay, child) {
+
+		/* default is add */
+		remove = 0;
+		cname = child->name;
+		if (*cname == '-') {	/* skip, - notes removal */
+			cname++;
+			remove = 1;
+		}
+
+		/* special case for nodes with a suffix */
+		suffix = strrchr(child->full_name, '@');
+		if (suffix != NULL) {
+			cname = kbasename(child->full_name);
+			WARN_ON(cname == NULL);	/* sanity check */
+			if (cname == NULL)
+				continue;
+			if (*cname == '-')
+				cname++;
+		}
+
+		tchild = of_get_child_by_name(target, cname);
+		if (tchild != NULL) {
+
+			if (!remove) {
+
+				/* apply overlay recursively */
+				ret = of_overlay_apply_one(tchild, child);
+				of_node_put(tchild);
+
+				if (ret != 0)
+					return ret;
+
+			} else {
+
+				ret = of_detach_node(tchild);
+				of_node_put(tchild);
+			}
+
+		} else {
+
+			if (!remove) {
+				full_name = kasprintf(GFP_KERNEL, "%s/%s",
+						target->full_name, cname);
+				if (full_name == NULL)
+					return -ENOMEM;
+
+				/* create empty tree as a target */
+				tchild = __of_create_empty_node(cname,
+						child->type, full_name,
+						child->phandle, GFP_KERNEL);
+
+				/* free either way */
+				kfree(full_name);
+
+				if (tchild == NULL)
+					return -ENOMEM;
+
+				/* point to parent */
+				tchild->parent = target;
+
+				ret = of_attach_node(tchild);
+				if (ret != 0)
+					return ret;
+
+				/* apply the overlay */
+				ret = of_overlay_apply_one(tchild, child);
+				if (ret != 0) {
+					__of_free_tree(tchild);
+					return ret;
+				}
+			}
+		}
+	}
+
+	return 0;
+}
+
+/**
+ * Lookup an overlay device entry
+ */
+struct of_overlay_device_entry *of_overlay_device_entry_lookup(
+		struct of_overlay_info *ovinfo, struct device_node *node)
+{
+	struct of_overlay_device_entry *de;
+
+	/* no need for locks, we'de under the ovinfo->lock */
+	list_for_each_entry(de, &ovinfo->de_list, node) {
+		if (de->np == node)
+			return de;
+	}
+	return NULL;
+}
+
+/**
+ * Add an overlay log entry
+ */
+static int of_overlay_log_entry_entry_add(struct of_overlay_info *ovinfo,
+		unsigned long action, struct device_node *dn,
+		struct property *prop)
+{
+	struct of_overlay_log_entry *le;
+
+	/* check */
+	if (ovinfo == NULL || dn == NULL)
+		return -EINVAL;
+
+	le = kzalloc(sizeof(*le), GFP_KERNEL);
+	if (le == NULL) {
+		pr_err("%s: Failed to allocate\n", __func__);
+		return -ENOMEM;
+	}
+
+	/* get a reference to the node */
+	le->action = action;
+	le->np = of_node_get(dn);
+	le->prop = prop;
+
+	if (action == OF_RECONFIG_UPDATE_PROPERTY && prop)
+		le->old_prop = of_find_property(dn, prop->name, NULL);
+
+	list_add_tail(&le->node, &ovinfo->le_list);
+
+	return 0;
+}
+
+/**
+ * Add an overlay device entry
+ */
+static void of_overlay_device_entry_entry_add(struct of_overlay_info *ovinfo,
+		struct device_node *node,
+		struct platform_device *pdev, struct i2c_client *client,
+		int prevstate, int state)
+{
+	struct of_overlay_device_entry *de;
+	int fresh;
+
+	/* check */
+	if (ovinfo == NULL)
+		return;
+
+	fresh = 0;
+	de = of_overlay_device_entry_lookup(ovinfo, node);
+	if (de == NULL) {
+		de = kzalloc(sizeof(*de), GFP_KERNEL);
+		if (de == NULL) {
+			pr_err("%s: Failed to allocate\n", __func__);
+			return;
+		}
+		fresh = 1;
+		de->prevstate = -1;
+	}
+
+	if (de->np == NULL)
+		de->np = of_node_get(node);
+	if (de->pdev == NULL && pdev)
+		de->pdev = of_dev_get(pdev);
+	if (de->client == NULL && client)
+		de->client = i2c_use_client(client);
+	if (fresh)
+		de->prevstate = prevstate;
+	de->state = state;
+
+	if (fresh)
+		list_add_tail(&de->node, &ovinfo->de_list);
+}
+
+/**
+ * Overlay OF notifier
+ *
+ * Called every time there's a property/node modification
+ * Every modification causes a log entry addition, while
+ * any modification that causes a node's state to change
+ * from/to disabled to/from enabled causes a device entry
+ * addition.
+ */
+static int of_overlay_notify(struct notifier_block *nb,
+				unsigned long action, void *arg)
+{
+	struct of_overlay_info *ovinfo;
+	struct device_node *node;
+	struct property *prop, *sprop, *cprop;
+	struct of_prop_reconfig *pr;
+	struct platform_device *pdev;
+	struct i2c_client *client;
+	struct device_node *tnode;
+	int depth;
+	int prevstate, state;
+	int err = 0;
+
+	ovinfo = container_of(nb, struct of_overlay_info, notifier);
+
+	/* prep vars */
+	switch (action) {
+	case OF_RECONFIG_ATTACH_NODE:
+	case OF_RECONFIG_DETACH_NODE:
+		node = arg;
+		if (node == NULL)
+			return notifier_from_errno(-EINVAL);
+		prop = NULL;
+		break;
+	case OF_RECONFIG_ADD_PROPERTY:
+	case OF_RECONFIG_REMOVE_PROPERTY:
+	case OF_RECONFIG_UPDATE_PROPERTY:
+		pr = arg;
+		if (pr == NULL)
+			return notifier_from_errno(-EINVAL);
+		node = pr->dn;
+		if (node == NULL)
+			return notifier_from_errno(-EINVAL);
+		prop = pr->prop;
+		if (prop == NULL)
+			return notifier_from_errno(-EINVAL);
+		break;
+	default:
+		return notifier_from_errno(0);
+	}
+
+	/* add to the log */
+	err = of_overlay_log_entry_entry_add(ovinfo, action, node, prop);
+	if (err != 0)
+		return notifier_from_errno(err);
+
+	/* come up with the device entry (if any) */
+	pdev = NULL;
+	client = NULL;
+	state = 0;
+	prevstate = 0;
+
+	/* determine the state the node will end up */
+	switch (action) {
+	case OF_RECONFIG_ATTACH_NODE:
+		/* we demand that a compatible node is present */
+		state = of_find_property(node, "compatible", NULL) &&
+			of_device_is_available(node);
+		break;
+	case OF_RECONFIG_DETACH_NODE:
+		prevstate = of_find_property(node, "compatible", NULL) &&
+			of_device_is_available(node);
+		state = 0;
+		pdev = of_find_device_by_node(node);
+		client = of_find_i2c_device_by_node(node);
+		break;
+	case OF_RECONFIG_ADD_PROPERTY:
+	case OF_RECONFIG_REMOVE_PROPERTY:
+	case OF_RECONFIG_UPDATE_PROPERTY:
+		/* either one cause a change in state */
+		if (strcmp(prop->name, "status") != 0 &&
+				strcmp(prop->name, "compatible") != 0)
+			return notifier_from_errno(0);
+
+		if (strcmp(prop->name, "status") == 0) {
+			/* status */
+			cprop = of_find_property(node, "compatible", NULL);
+			sprop = action != OF_RECONFIG_REMOVE_PROPERTY ?
+				prop : NULL;
+		} else {
+			/* compatible */
+			sprop = of_find_property(node, "status", NULL);
+			cprop = action != OF_RECONFIG_REMOVE_PROPERTY ?
+				prop : NULL;
+		}
+
+		prevstate = of_find_property(node, "compatible", NULL) &&
+			of_device_is_available(node);
+		state = cprop && cprop->length > 0 &&
+			    (!sprop || (sprop->length > 0 &&
+				(strcmp(sprop->value, "okay") == 0 ||
+				 strcmp(sprop->value, "ok") == 0)));
+		break;
+
+	default:
+		return notifier_from_errno(0);
+	}
+
+	/* find depth */
+	depth = 1;
+	tnode = node;
+	while (tnode != NULL && tnode != ovinfo->target) {
+		tnode = tnode->parent;
+		depth++;
+	}
+
+	/* respect overlay's maximum depth */
+	if (ovinfo->device_depth != 0 && depth > ovinfo->device_depth) {
+		pr_debug("OF: skipping device creation for node=%s depth=%d\n",
+				node->name, depth);
+		goto out;
+	}
+
+	if (state == 0) {
+		pdev = of_find_device_by_node(node);
+		client = of_find_i2c_device_by_node(node);
+	}
+
+	of_overlay_device_entry_entry_add(ovinfo, node, pdev, client,
+			prevstate, state);
+out:
+
+	return notifier_from_errno(err);
+}
+
+/**
+ * Prepare for the overlay, for now it just registers the
+ * notifier.
+ */
+static int of_overlay_prep_one(struct of_overlay_info *ovinfo)
+{
+	int err;
+
+	err = of_reconfig_notifier_register(&ovinfo->notifier);
+	if (err != 0) {
+		pr_err("%s: failed to register notifier for '%s'\n",
+			__func__, ovinfo->target->full_name);
+		return err;
+	}
+	return 0;
+}
+
+static int of_overlay_device_entry_change(struct of_overlay_info *ovinfo,
+		struct of_overlay_device_entry *de, int revert)
+{
+	struct i2c_adapter *adap = NULL;
+	struct i2c_client *client;
+	struct platform_device *pdev, *parent_pdev = NULL;
+	int state;
+
+	state = !!de->state ^ !!revert;
+
+	if (de->np && de->np->parent) {
+		pr_debug("%s: parent is %s\n",
+				__func__, de->np->parent->full_name);
+		adap = of_find_i2c_adapter_by_node(de->np->parent);
+		if (adap == NULL)
+			parent_pdev = of_find_device_by_node(de->np->parent);
+	}
+
+	if (state) {
+
+		/* try to see if it's an I2C client node */
+		if (adap == NULL) {
+
+			pr_debug("%s: creating new platform device "
+					"new_node='%s' %p\n",
+					__func__, de->np->full_name, de->np);
+
+			pdev = of_platform_device_create(de->np, NULL,
+					parent_pdev ? &parent_pdev->dev : NULL);
+			if (pdev == NULL) {
+				pr_warn("%s: Failed to create platform device "
+						"for '%s'\n",
+						__func__, de->np->full_name);
+			} else
+				de->pdev = pdev;
+
+		} else {
+
+			client = of_find_i2c_device_by_node(de->np);
+			if (client != NULL) {
+				/* bus already created the device; do nothing */
+				put_device(&client->dev);
+			} else {
+				pr_debug("%s: creating new i2c_client device "
+						"new_node='%s' %p\n",
+						__func__, de->np->full_name, de->np);
+
+				client = of_i2c_register_device(adap, de->np);
+
+				if (client == NULL) {
+					pr_warn("%s: Failed to create i2c client device "
+							"for '%s'\n",
+							__func__, de->np->full_name);
+				} else
+					de->client = client;
+			}
+		}
+
+	} else {
+
+		if (de->pdev) {
+			pr_debug("%s: removing pdev %s\n", __func__,
+					dev_name(&de->pdev->dev));
+			platform_device_unregister(de->pdev);
+			de->pdev = NULL;
+		}
+
+		if (de->client) {
+			pr_debug("%s: removing i2c client %s\n", __func__,
+					dev_name(&de->client->dev));
+			i2c_unregister_device(de->client);
+			de->client = NULL;
+		}
+	}
+
+	if (adap)
+		put_device(&adap->dev);
+
+	if (parent_pdev)
+		of_dev_put(parent_pdev);
+
+	return 0;
+}
+
+/**
+ * Revert one overlay
+ * Either due to an error, or due to normal overlay removal.
+ * Using the log entries, we revert any change to the live tree.
+ * In the same manner, using the device entries we enable/disable
+ * the platform devices appropriately.
+ */
+static void of_overlay_revert_one(struct of_overlay_info *ovinfo)
+{
+	struct of_overlay_device_entry *de, *den;
+	struct of_overlay_log_entry *le, *len;
+	struct property *prop, **propp;
+	int ret;
+	unsigned long flags;
+
+	if (!ovinfo || !ovinfo->target || !ovinfo->overlay)
+		return;
+
+	pr_debug("%s: Reverting overlay on '%s'\n", __func__,
+			ovinfo->target->full_name);
+
+	/* overlay applied correctly, now create/destroy pdevs */
+	list_for_each_entry_safe_reverse(de, den, &ovinfo->de_list, node) {
+		of_overlay_device_entry_change(ovinfo, de, 1);
+		of_node_put(de->np);
+		list_del(&de->node);
+		kfree(de);
+	}
+
+	list_for_each_entry_safe_reverse(le, len, &ovinfo->le_list, node) {
+
+		ret = 0;
+		switch (le->action) {
+		case OF_RECONFIG_ATTACH_NODE:
+			pr_debug("Reverting ATTACH_NODE %s\n",
+					le->np->full_name);
+			ret = of_detach_node(le->np);
+			break;
+
+		case OF_RECONFIG_DETACH_NODE:
+			pr_debug("Reverting DETACH_NODE %s\n",
+					le->np->full_name);
+			ret = of_attach_node(le->np);
+			break;
+
+		case OF_RECONFIG_ADD_PROPERTY:
+			pr_debug("Reverting ADD_PROPERTY %s %s\n",
+					le->np->full_name, le->prop->name);
+			ret = of_remove_property(le->np, le->prop);
+			break;
+
+		case OF_RECONFIG_REMOVE_PROPERTY:
+		case OF_RECONFIG_UPDATE_PROPERTY:
+
+			pr_debug("Reverting %s_PROPERTY %s %s\n",
+				le->action == OF_RECONFIG_REMOVE_PROPERTY ?
+					"REMOVE" : "UPDATE",
+					le->np->full_name, le->prop->name);
+
+			/* property is possibly on deadprops (avoid alloc) */
+			raw_spin_lock_irqsave(&devtree_lock, flags);
+			prop = le->action == OF_RECONFIG_REMOVE_PROPERTY ?
+				le->prop : le->old_prop;
+			propp = &le->np->deadprops;
+			while (*propp != NULL) {
+				if (*propp == prop)
+					break;
+				propp = &(*propp)->next;
+			}
+			if (*propp != NULL) {
+				/* remove it from deadprops */
+				(*propp)->next = prop->next;
+				raw_spin_unlock_irqrestore(&devtree_lock,
+						flags);
+			} else {
+				raw_spin_unlock_irqrestore(&devtree_lock,
+						flags);
+				/* not found, just make a copy */
+				prop = __of_copy_property(prop, GFP_KERNEL);
+				if (prop == NULL) {
+					pr_err("%s: Failed to copy property\n",
+							__func__);
+					break;
+				}
+			}
+
+			if (le->action == OF_RECONFIG_REMOVE_PROPERTY)
+				ret = of_add_property(le->np, prop);
+			else
+				ret = of_update_property(le->np, prop);
+			break;
+
+		default:
+			/* nothing */
+			break;
+		}
+
+		if (ret != 0)
+			pr_err("%s: revert on node %s Failed!\n",
+					__func__, le->np->full_name);
+
+		of_node_put(le->np);
+
+		list_del(&le->node);
+
+		kfree(le);
+	}
+}
+
+/**
+ * Perform the post overlay work.
+ *
+ * We unregister the notifier, and in the case on an error we
+ * revert the overlay.
+ * If the overlay applied correctly, we iterare over the device entries
+ * and create/destroy the platform devices appropriately.
+ */
+static int of_overlay_post_one(struct of_overlay_info *ovinfo, int err)
+{
+	struct of_overlay_device_entry *de, *den;
+
+	of_reconfig_notifier_unregister(&ovinfo->notifier);
+
+	if (err != 0) {
+		/* revert this (possible partially applied) overlay */
+		of_overlay_revert_one(ovinfo);
+		return 0;
+	}
+
+	/* overlay applied correctly, now create/destroy pdevs */
+	list_for_each_entry_safe(de, den, &ovinfo->de_list, node) {
+
+		/* no state change? just remove this entry */
+		if (de->prevstate == de->state) {
+			of_node_put(de->np);
+			list_del(&de->node);
+			kfree(de);
+		} else {
+			of_overlay_device_entry_change(ovinfo, de, 0);
+		}
+	}
+
+	return 0;
+}
+
+/**
+ * of_overlay	- Apply @count overlays pointed at by @ovinfo_tab
+ * @count:	Number of of_overlay_info's
+ * @ovinfo_tab:	Array of overlay_info's to apply
+ *
+ * Applies the overlays given, while handling all error conditions
+ * appropriately. Either the operation succeeds, or if it fails the
+ * live tree is reverted to the state before the attempt.
+ * Returns 0, or an error if the overlay attempt failed.
+ */
+int of_overlay(int count, struct of_overlay_info *ovinfo_tab)
+{
+	struct of_overlay_info *ovinfo;
+	int i, err;
+
+	if (!ovinfo_tab)
+		return -EINVAL;
+
+	/* first we apply the overlays atomically */
+	for (i = 0; i < count; i++) {
+
+		ovinfo = &ovinfo_tab[i];
+
+		mutex_lock(&ovinfo->lock);
+
+		err = of_overlay_prep_one(ovinfo);
+		if (err == 0)
+			err = of_overlay_apply_one(ovinfo->target,
+					ovinfo->overlay);
+		of_overlay_post_one(ovinfo, err);
+
+		mutex_unlock(&ovinfo->lock);
+
+		if (err != 0) {
+			pr_err("%s: overlay failed '%s'\n",
+				__func__, ovinfo->target->full_name);
+			goto err_fail;
+		}
+	}
+
+	return 0;
+
+err_fail:
+	while (--i >= 0) {
+		ovinfo = &ovinfo_tab[i];
+
+		mutex_lock(&ovinfo->lock);
+		of_overlay_revert_one(ovinfo);
+		mutex_unlock(&ovinfo->lock);
+	}
+
+	return err;
+}
+
+/**
+ * of_overlay_revert	- Revert a previously applied overlay
+ * @count:	Number of of_overlay_info's
+ * @ovinfo_tab:	Array of overlay_info's to apply
+ *
+ * Revert a previous overlay. The state of the live tree
+ * is reverted to the one before the overlay.
+ * Returns 0, or an error if the overlay table is not given.
+ */
+int of_overlay_revert(int count, struct of_overlay_info *ovinfo_tab)
+{
+	struct of_overlay_info *ovinfo;
+	int i;
+
+	if (!ovinfo_tab)
+		return -EINVAL;
+
+	/* revert the overlays in reverse */
+	for (i = count - 1; i >= 0; i--) {
+
+		ovinfo = &ovinfo_tab[i];
+
+		mutex_lock(&ovinfo->lock);
+		of_overlay_revert_one(ovinfo);
+		mutex_unlock(&ovinfo->lock);
+
+	}
+
+	return 0;
+}
+
+/**
+ * of_init_overlay_info	- Initialize a single of_overlay_info structure
+ * @ovinfo:	Pointer to the overlay info structure to initialize
+ *
+ * Initialize a single overlay info structure.
+ */
+void of_init_overlay_info(struct of_overlay_info *ovinfo)
+{
+	memset(ovinfo, 0, sizeof(ovinfo));
+	mutex_init(&ovinfo->lock);
+	INIT_LIST_HEAD(&ovinfo->de_list);
+	INIT_LIST_HEAD(&ovinfo->le_list);
+
+	ovinfo->notifier.notifier_call = of_overlay_notify;
+}
+
+/**
+ * of_fill_overlay_info	- Fill an overlay info structure
+ * @info_node:	Device node containing the overlay
+ * @ovinfo:	Pointer to the overlay info structure to fill
+ *
+ * Fills an overlay info structure with the overlay information
+ * from a device node. This device node must have a target property
+ * which contains a phandle of the overlay target node, and an
+ * __overlay__ child node which has the overlay contents.
+ * Both ovinfo->target & ovinfo->overlay have their references taken.
+ *
+ * Returns 0 on success, or a negative error value.
+ */
+int of_fill_overlay_info(struct device_node *info_node,
+		struct of_overlay_info *ovinfo)
+{
+	u32 val;
+	int ret;
+
+	if (!info_node || !ovinfo)
+		return -EINVAL;
+
+	ret = of_property_read_u32(info_node, "target", &val);
+	if (ret != 0)
+		goto err_fail;
+
+	ovinfo->target = of_find_node_by_phandle(val);
+	if (ovinfo->target == NULL)
+		goto err_fail;
+
+	ovinfo->overlay = of_get_child_by_name(info_node, "__overlay__");
+	if (ovinfo->overlay == NULL)
+		goto err_fail;
+
+	ret = of_property_read_u32(info_node, "depth", &val);
+	if (ret == 0)
+		ovinfo->device_depth = val;
+	else
+		ovinfo->device_depth = 0;
+
+
+	return 0;
+
+err_fail:
+	of_node_put(ovinfo->target);
+	of_node_put(ovinfo->overlay);
+
+	memset(ovinfo, 0, sizeof(*ovinfo));
+	return -EINVAL;
+}
+
+/**
+ * of_build_overlay_info	- Build an overlay info array
+ * @tree:	Device node containing all the overlays
+ * @cntp:	Pointer to where the overlay info count will be help
+ * @ovinfop:	Pointer to the pointer of an overlay info structure.
+ *
+ * Helper function that given a tree containing overlay information,
+ * allocates and builds an overlay info array containing it, ready
+ * for use using of_overlay.
+ *
+ * Returns 0 on success with the @cntp @ovinfop pointers valid,
+ * while on error a negative error value is returned.
+ */
+int of_build_overlay_info(struct device_node *tree,
+		int *cntp, struct of_overlay_info **ovinfop)
+{
+	struct device_node *node;
+	struct of_overlay_info *ovinfo;
+	int cnt, err;
+
+	if (tree == NULL || cntp == NULL || ovinfop == NULL)
+		return -EINVAL;
+
+	/* worst case; every child is a node */
+	cnt = 0;
+	for_each_child_of_node(tree, node)
+		cnt++;
+
+	ovinfo = kzalloc(cnt * sizeof(*ovinfo), GFP_KERNEL);
+	if (ovinfo == NULL)
+		return -ENOMEM;
+
+	cnt = 0;
+	for_each_child_of_node(tree, node) {
+
+		of_init_overlay_info(&ovinfo[cnt]);
+		err = of_fill_overlay_info(node, &ovinfo[cnt]);
+		if (err == 0)
+			cnt++;
+	}
+
+	/* if nothing filled, return error */
+	if (cnt == 0) {
+		kfree(ovinfo);
+		return -ENODEV;
+	}
+
+	*cntp = cnt;
+	*ovinfop = ovinfo;
+
+	return 0;
+}
+
+/**
+ * of_free_overlay_info	- Free an overlay info array
+ * @count:	Number of of_overlay_info's
+ * @ovinfo_tab:	Array of overlay_info's to free
+ *
+ * Releases the memory of a previously allocate ovinfo array
+ * by of_build_overlay_info.
+ * Returns 0, or an error if the arguments are bogus.
+ */
+int of_free_overlay_info(int count, struct of_overlay_info *ovinfo_tab)
+{
+	struct of_overlay_info *ovinfo;
+	int i;
+
+	if (!ovinfo_tab || count < 0)
+		return -EINVAL;
+
+	/* do it in reverse */
+	for (i = count - 1; i >= 0; i--) {
+		ovinfo = &ovinfo_tab[i];
+
+		of_node_put(ovinfo->target);
+		of_node_put(ovinfo->overlay);
+	}
+	kfree(ovinfo_tab);
+
+	return 0;
+}
diff --git a/include/linux/of.h b/include/linux/of.h
index 22d42e5..d9c8130 100644
--- a/include/linux/of.h
+++ b/include/linux/of.h
@@ -23,6 +23,7 @@
 #include <linux/spinlock.h>
 #include <linux/topology.h>
 #include <linux/notifier.h>
+#include <linux/i2c.h>
 
 #include <asm/byteorder.h>
 #include <asm/errno.h>
@@ -738,4 +739,116 @@ static inline int of_resolve(struct device_node *resolve)
 
 #endif
 
+/**
+ * Overlay support
+ */
+
+/**
+ * struct of_overlay_log_entry	- Holds a DT log entry
+ * @node:	list_head for the log list
+ * @action:	notifier action
+ * @np:		pointer to the device node affected
+ * @prop:	pointer to the property affected
+ * @old_prop:	hold a pointer to the original property
+ *
+ * Every modification of the device tree during application of the
+ * overlay is held in a list of of_overlay_log_entry structures.
+ * That way we can recover from a partial application, or we can
+ * revert the overlay properly.
+ */
+struct of_overlay_log_entry {
+	struct list_head node;
+	unsigned long action;
+	struct device_node *np;
+	struct property *prop;
+	struct property *old_prop;
+};
+
+/**
+ * struct of_overlay_device_entry	- Holds an overlay device entry
+ * @node:	list_head for the device list
+ * @np:		device node pointer to the device node affected
+ * @pdev:	pointer to the platform device affected
+ * @client:	pointer to the I2C client device affected
+ * @state:	new device state
+ * @prevstate:	previous device state
+ *
+ * When the overlay results in a device node's state to change this
+ * fact is recorded in a list of device entries. After the overlay
+ * is applied we can create/destroy the platform devices according
+ * to the new state of the live tree.
+ */
+struct of_overlay_device_entry {
+	struct list_head node;
+	struct device_node *np;
+	struct platform_device *pdev;
+	struct i2c_client *client;
+	int prevstate;
+	int state;
+};
+
+/**
+ * struct of_overlay_info	- Holds a single overlay info
+ * @target:	target of the overlay operation
+ * @overlay:	pointer to the overlay contents node
+ * @lock:	Lock to hold when accessing the lists
+ * @le_list:	List of the overlay logs
+ * @de_list:	List of the overlay records
+ * @notifier:	of reconfiguration notifier
+ *
+ * Holds a single overlay state, including all the overlay logs &
+ * records.
+ */
+struct of_overlay_info {
+	struct device_node *target;
+	struct device_node *overlay;
+	struct mutex lock;
+	struct list_head le_list;
+	struct list_head de_list;
+	struct notifier_block notifier;
+	int device_depth;
+};
+
+#ifdef CONFIG_OF_OVERLAY
+
+int of_overlay(int count, struct of_overlay_info *ovinfo_tab);
+int of_overlay_revert(int count, struct of_overlay_info *ovinfo_tab);
+
+int of_fill_overlay_info(struct device_node *info_node,
+		struct of_overlay_info *ovinfo);
+int of_build_overlay_info(struct device_node *tree,
+		int *cntp, struct of_overlay_info **ovinfop);
+int of_free_overlay_info(int cnt, struct of_overlay_info *ovinfo);
+
+#else
+
+static inline int of_overlay(int count, struct of_overlay_info *ovinfo_tab)
+{
+	return -ENOTSUPP;
+}
+
+static inline int of_overlay_revert(int count, struct of_overlay_info *ovinfo_tab)
+{
+	return -ENOTSUPP;
+}
+
+static inline int of_fill_overlay_info(struct device_node *info_node,
+		struct of_overlay_info *ovinfo)
+{
+	return -ENOTSUPP;
+}
+
+static inline int of_build_overlay_info(struct device_node *tree,
+		int *cntp, struct of_overlay_info **ovinfop)
+{
+	return -ENOTSUPP;
+}
+
+int of_free_overlay_info(int cnt, struct of_overlay_info *ovinfo)
+{
+	return -ENOTSUPP;
+}
+
+#endif
+
 #endif /* _LINUX_OF_H */
-- 
1.9.1