Re: [PATCH 2/3] OF: Introduce DT overlay support.

[Alexander Sverdlin <alexander.sverdlin@nsn.com>]

Hi!

On 05/11/13 19:41, ext Pantelis Antoniou wrote:
> 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>

Reviewed-by: Alexander Sverdlin <alexander.sverdlin@nsn.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..5289cbb
> --- /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..5bed1f4
> --- /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/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 */
> 

-- 
Best regards,
Alexander Sverdlin.