5 files changed, 734 insertions, 0 deletions

diff --git a/Documentation/devicetree/overlay-notes.txt b/Documentation/devicetree/overlay-notes.txt
new file mode 100644
index 000000000000..30ae758e3eef
--- /dev/null
+++ b/Documentation/devicetree/overlay-notes.txt
@@ -0,0 +1,133 @@
+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 API is quite easy to use.
+
+1. Call of_overlay_create() to create and apply an overlay. The return value
+is a cookie identifying this overlay.
+
+2. Call of_overlay_destroy() to remove and cleanup the overlay previously
+created via the call to of_overlay_create(). Removal of an overlay that
+is stacked by another will not be permitted.
+
+Finally, if you need to remove all overlays in one-go, just call
+of_overlay_destroy_all() which will remove every single one in the correct
+order.
+
+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>;       /* phandle target of the overlay */
+        or
+                target-path="/path";    /* target path of the overlay */
+
+                __overlay__ {
+                        property-a;     /* add property-a to the target */
+                        node-a {        /* add to an existing, or create a node-a */
+                                ...
+                        };
+                };
+        }
+        fragment@1 {    /* second child node */
+                ...
+        };
+        /* more fragments follow */
+}
+
+Using the non-phandle based target method allows one to use a base DT which does
+not contain a __symbols__ node, i.e. it was not compiled with the -@ option.
+The __symbols__ node is only required for the target=<phandle> method, since it
+contains the information required to map from a phandle to a tree location.
diff --git a/drivers/of/Kconfig b/drivers/of/Kconfig
index fbe8f8d418f7..18b2e2539f84 100644
--- a/drivers/of/Kconfig
+++ b/drivers/of/Kconfig
@@ -84,4 +84,11 @@ config OF_RESERVED_MEM
 config OF_RESOLVE
         bool
 
+config OF_OVERLAY
+        bool
+        depends on OF
+        select OF_DYNAMIC
+        select OF_DEVICE
+        select OF_RESOLVE
+
 endmenu # OF
diff --git a/drivers/of/Makefile b/drivers/of/Makefile
index d90553fcd37f..7563f36c71db 100644
--- a/drivers/of/Makefile
+++ b/drivers/of/Makefile
@@ -14,6 +14,7 @@ obj-$(CONFIG_OF_PCI_IRQ)  += of_pci_irq.o
 obj-$(CONFIG_OF_MTD)    += of_mtd.o
 obj-$(CONFIG_OF_RESERVED_MEM) += of_reserved_mem.o
 obj-$(CONFIG_OF_RESOLVE)  += resolver.o
+obj-$(CONFIG_OF_OVERLAY) += overlay.o
 
 CFLAGS_fdt.o = -I$(src)/../../scripts/dtc/libfdt
 CFLAGS_fdt_address.o = -I$(src)/../../scripts/dtc/libfdt
diff --git a/drivers/of/overlay.c b/drivers/of/overlay.c
new file mode 100644
index 000000000000..ea63fbd228ed
--- /dev/null
+++ b/drivers/of/overlay.c
@@ -0,0 +1,562 @@
+/*
+ * 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/string.h>
+#include <linux/ctype.h>
+#include <linux/errno.h>
+#include <linux/string.h>
+#include <linux/slab.h>
+#include <linux/err.h>
+
+#include "of_private.h"
+
+/**
+ * struct of_overlay_info - Holds a single overlay info
+ * @target:     target of the overlay operation
+ * @overlay:    pointer to the overlay contents node
+ *
+ * Holds a single overlay state, including all the overlay logs &
+ * records.
+ */
+struct of_overlay_info {
+        struct device_node *target;
+        struct device_node *overlay;
+};
+
+/**
+ * struct of_overlay - Holds a complete overlay transaction
+ * @node:       List on which we are located
+ * @count:      Count of ovinfo structures
+ * @ovinfo_tab: Overlay info table (count sized)
+ * @cset:       Changeset to be used
+ *
+ * Holds a complete overlay transaction
+ */
+struct of_overlay {
+        int id;
+        struct list_head node;
+        int count;
+        struct of_overlay_info *ovinfo_tab;
+        struct of_changeset cset;
+};
+
+static int of_overlay_apply_one(struct of_overlay *ov,
+                struct device_node *target, const struct device_node *overlay);
+
+static int of_overlay_apply_single_property(struct of_overlay *ov,
+                struct device_node *target, struct property *prop)
+{
+        struct property *propn, *tprop;
+
+        /* NOTE: Multiple changes of single properties not supported */
+        tprop = of_find_property(target, prop->name, NULL);
+
+        /* special properties are not meant to be updated (silent NOP) */
+        if (of_prop_cmp(prop->name, "name") == 0 ||
+            of_prop_cmp(prop->name, "phandle") == 0 ||
+            of_prop_cmp(prop->name, "linux,phandle") == 0)
+                return 0;
+
+        propn = __of_prop_dup(prop, GFP_KERNEL);
+        if (propn == NULL)
+                return -ENOMEM;
+
+        /* not found? add */
+        if (tprop == NULL)
+                return of_changeset_add_property(&ov->cset, target, propn);
+
+        /* found? update */
+        return of_changeset_update_property(&ov->cset, target, propn);
+}
+
+static int of_overlay_apply_single_device_node(struct of_overlay *ov,
+                struct device_node *target, struct device_node *child)
+{
+        const char *cname;
+        struct device_node *tchild, *grandchild;
+        int ret = 0;
+
+        cname = kbasename(child->full_name);
+        if (cname == NULL)
+                return -ENOMEM;
+
+        /* NOTE: Multiple mods of created nodes not supported */
+        tchild = of_get_child_by_name(target, cname);
+        if (tchild != NULL) {
+                /* apply overlay recursively */
+                ret = of_overlay_apply_one(ov, tchild, child);
+                of_node_put(tchild);
+        } else {
+                /* create empty tree as a target */
+                tchild = __of_node_dup(child, "%s/%s", target->full_name, cname);
+                if (!tchild)
+                        return -ENOMEM;
+
+                /* point to parent */
+                tchild->parent = target;
+
+                ret = of_changeset_attach_node(&ov->cset, tchild);
+                if (ret)
+                        return ret;
+
+                ret = of_overlay_apply_one(ov, tchild, child);
+                if (ret)
+                        return ret;
+
+                /* The properties are already copied, now do the child nodes */
+                for_each_child_of_node(child, grandchild) {
+                        ret = of_overlay_apply_single_device_node(ov, tchild, grandchild);
+                        if (ret) {
+                                pr_err("%s: Failed to apply single node @%s/%s\n",
+                                        __func__, tchild->full_name,
+                                        grandchild->name);
+                                return ret;
+                        }
+                }
+        }
+
+        return ret;
+}
+
+/*
+ * Apply a single overlay node recursively.
+ *
+ * Note that the in case of an error the target node is left
+ * in a inconsistent state. Error recovery should be performed
+ * by using the changeset.
+ */
+static int of_overlay_apply_one(struct of_overlay *ov,
+                struct device_node *target, const struct device_node *overlay)
+{
+        struct device_node *child;
+        struct property *prop;
+        int ret;
+
+        for_each_property_of_node(overlay, prop) {
+                ret = of_overlay_apply_single_property(ov, target, prop);
+                if (ret) {
+                        pr_err("%s: Failed to apply prop @%s/%s\n",
+                                __func__, target->full_name, prop->name);
+                        return ret;
+                }
+        }
+
+        for_each_child_of_node(overlay, child) {
+                ret = of_overlay_apply_single_device_node(ov, target, child);
+                if (ret != 0) {
+                        pr_err("%s: Failed to apply single node @%s/%s\n",
+                                        __func__, target->full_name,
+                                        child->name);
+                        return ret;
+                }
+        }
+
+        return 0;
+}
+
+/**
+ * of_overlay_apply() - Apply @count overlays pointed at by @ovinfo_tab
+ * @ov:         Overlay 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.
+ */
+static int of_overlay_apply(struct of_overlay *ov)
+{
+        int i, err;
+
+        /* first we apply the overlays atomically */
+        for (i = 0; i < ov->count; i++) {
+                struct of_overlay_info *ovinfo = &ov->ovinfo_tab[i];
+
+                err = of_overlay_apply_one(ov, ovinfo->target, ovinfo->overlay);
+                if (err != 0) {
+                        pr_err("%s: overlay failed '%s'\n",
+                                __func__, ovinfo->target->full_name);
+                        return err;
+                }
+        }
+
+        return 0;
+}
+
+/*
+ * Find the target node using a number of different strategies
+ * in order of preference
+ *
+ * "target" property containing the phandle of the target
+ * "target-path" property containing the path of the target
+ */
+static struct device_node *find_target_node(struct device_node *info_node)
+{
+        const char *path;
+        u32 val;
+        int ret;
+
+        /* first try to go by using the target as a phandle */
+        ret = of_property_read_u32(info_node, "target", &val);
+        if (ret == 0)
+                return of_find_node_by_phandle(val);
+
+        /* now try to locate by path */
+        ret = of_property_read_string(info_node, "target-path", &path);
+        if (ret == 0)
+                return of_find_node_by_path(path);
+
+        pr_err("%s: Failed to find target for node %p (%s)\n", __func__,
+                info_node, info_node->name);
+
+        return NULL;
+}
+
+/**
+ * of_fill_overlay_info() - Fill an overlay info structure
+ * @ov          Overlay to fill
+ * @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.
+ */
+static int of_fill_overlay_info(struct of_overlay *ov,
+                struct device_node *info_node, struct of_overlay_info *ovinfo)
+{
+        ovinfo->overlay = of_get_child_by_name(info_node, "__overlay__");
+        if (ovinfo->overlay == NULL)
+                goto err_fail;
+
+        ovinfo->target = find_target_node(info_node);
+        if (ovinfo->target == NULL)
+                goto err_fail;
+
+        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
+ * @ov          Overlay to build
+ * @tree:       Device node containing all the overlays
+ *
+ * Helper function that given a tree containing overlay information,
+ * allocates and builds an overlay info array containing it, ready
+ * for use using of_overlay_apply.
+ *
+ * Returns 0 on success with the @cntp @ovinfop pointers valid,
+ * while on error a negative error value is returned.
+ */
+static int of_build_overlay_info(struct of_overlay *ov,
+                struct device_node *tree)
+{
+        struct device_node *node;
+        struct of_overlay_info *ovinfo;
+        int cnt, err;
+
+        /* worst case; every child is a node */
+        cnt = 0;
+        for_each_child_of_node(tree, node)
+                cnt++;
+
+        ovinfo = kcalloc(cnt, sizeof(*ovinfo), GFP_KERNEL);
+        if (ovinfo == NULL)
+                return -ENOMEM;
+
+        cnt = 0;
+        for_each_child_of_node(tree, node) {
+                memset(&ovinfo[cnt], 0, sizeof(*ovinfo));
+                err = of_fill_overlay_info(ov, node, &ovinfo[cnt]);
+                if (err == 0)
+                        cnt++;
+        }
+
+        /* if nothing filled, return error */
+        if (cnt == 0) {
+                kfree(ovinfo);
+                return -ENODEV;
+        }
+
+        ov->count = cnt;
+        ov->ovinfo_tab = ovinfo;
+
+        return 0;
+}
+
+/**
+ * of_free_overlay_info() - Free an overlay info array
+ * @ov          Overlay to free the overlay info from
+ * @ovinfo_tab: Array of overlay_info's to free
+ *
+ * Releases the memory of a previously allocated ovinfo array
+ * by of_build_overlay_info.
+ * Returns 0, or an error if the arguments are bogus.
+ */
+static int of_free_overlay_info(struct of_overlay *ov)
+{
+        struct of_overlay_info *ovinfo;
+        int i;
+
+        /* do it in reverse */
+        for (i = ov->count - 1; i >= 0; i--) {
+                ovinfo = &ov->ovinfo_tab[i];
+
+                of_node_put(ovinfo->target);
+                of_node_put(ovinfo->overlay);
+        }
+        kfree(ov->ovinfo_tab);
+
+        return 0;
+}
+
+static LIST_HEAD(ov_list);
+static DEFINE_IDR(ov_idr);
+
+/**
+ * of_overlay_create() - Create and apply an overlay
+ * @tree:       Device node containing all the overlays
+ *
+ * Creates and applies an overlay while also keeping track
+ * of the overlay in a list. This list can be used to prevent
+ * illegal overlay removals.
+ *
+ * Returns the id of the created overlay, or an negative error number
+ */
+int of_overlay_create(struct device_node *tree)
+{
+        struct of_overlay *ov;
+        int err, id;
+
+        /* allocate the overlay structure */
+        ov = kzalloc(sizeof(*ov), GFP_KERNEL);
+        if (ov == NULL)
+                return -ENOMEM;
+        ov->id = -1;
+
+        INIT_LIST_HEAD(&ov->node);
+
+        of_changeset_init(&ov->cset);
+
+        mutex_lock(&of_mutex);
+
+        id = idr_alloc(&ov_idr, ov, 0, 0, GFP_KERNEL);
+        if (id < 0) {
+                pr_err("%s: idr_alloc() failed for tree@%s\n",
+                                __func__, tree->full_name);
+                err = id;
+                goto err_destroy_trans;
+        }
+        ov->id = id;
+
+        /* build the overlay info structures */
+        err = of_build_overlay_info(ov, tree);
+        if (err) {
+                pr_err("%s: of_build_overlay_info() failed for tree@%s\n",
+                                __func__, tree->full_name);
+                goto err_free_idr;
+        }
+
+        /* apply the overlay */
+        err = of_overlay_apply(ov);
+        if (err) {
+                pr_err("%s: of_overlay_apply() failed for tree@%s\n",
+                                __func__, tree->full_name);
+                goto err_abort_trans;
+        }
+
+        /* apply the changeset */
+        err = of_changeset_apply(&ov->cset);
+        if (err) {
+                pr_err("%s: of_changeset_apply() failed for tree@%s\n",
+                                __func__, tree->full_name);
+                goto err_revert_overlay;
+        }
+
+        /* add to the tail of the overlay list */
+        list_add_tail(&ov->node, &ov_list);
+
+        mutex_unlock(&of_mutex);
+
+        return id;
+
+err_revert_overlay:
+err_abort_trans:
+        of_free_overlay_info(ov);
+err_free_idr:
+        idr_remove(&ov_idr, ov->id);
+err_destroy_trans:
+        of_changeset_destroy(&ov->cset);
+        kfree(ov);
+        mutex_unlock(&of_mutex);
+
+        return err;
+}
+EXPORT_SYMBOL_GPL(of_overlay_create);
+
+/* check whether the given node, lies under the given tree */
+static int overlay_subtree_check(struct device_node *tree,
+                struct device_node *dn)
+{
+        struct device_node *child;
+
+        /* match? */
+        if (tree == dn)
+                return 1;
+
+        for_each_child_of_node(tree, child) {
+                if (overlay_subtree_check(child, dn))
+                        return 1;
+        }
+
+        return 0;
+}
+
+/* check whether this overlay is the topmost */
+static int overlay_is_topmost(struct of_overlay *ov, struct device_node *dn)
+{
+        struct of_overlay *ovt;
+        struct of_changeset_entry *ce;
+
+        list_for_each_entry_reverse(ovt, &ov_list, node) {
+                /* if we hit ourselves, we're done */
+                if (ovt == ov)
+                        break;
+
+                /* check against each subtree affected by this overlay */
+                list_for_each_entry(ce, &ovt->cset.entries, node) {
+                        if (overlay_subtree_check(ce->np, dn)) {
+                                pr_err("%s: #%d clashes #%d @%s\n",
+                                        __func__, ov->id, ovt->id,
+                                        dn->full_name);
+                                return 0;
+                        }
+                }
+        }
+
+        /* overlay is topmost */
+        return 1;
+}
+
+/*
+ * We can safely remove the overlay only if it's the top-most one.
+ * Newly applied overlays are inserted at the tail of the overlay list,
+ * so a top most overlay is the one that is closest to the tail.
+ *
+ * The topmost check is done by exploiting this property. For each
+ * affected device node in the log list we check if this overlay is
+ * the one closest to the tail. If another overlay has affected this
+ * device node and is closest to the tail, then removal is not permited.
+ */
+static int overlay_removal_is_ok(struct of_overlay *ov)
+{
+        struct of_changeset_entry *ce;
+
+        list_for_each_entry(ce, &ov->cset.entries, node) {
+                if (!overlay_is_topmost(ov, ce->np)) {
+                        pr_err("%s: overlay #%d is not topmost\n",
+                                        __func__, ov->id);
+                        return 0;
+                }
+        }
+
+        return 1;
+}
+
+/**
+ * of_overlay_destroy() - Removes an overlay
+ * @id: Overlay id number returned by a previous call to of_overlay_create
+ *
+ * Removes an overlay if it is permissible.
+ *
+ * Returns 0 on success, or an negative error number
+ */
+int of_overlay_destroy(int id)
+{
+        struct of_overlay *ov;
+        int err;
+
+        mutex_lock(&of_mutex);
+
+        ov = idr_find(&ov_idr, id);
+        if (ov == NULL) {
+                err = -ENODEV;
+                pr_err("%s: Could not find overlay #%d\n",
+                                __func__, id);
+                goto out;
+        }
+
+        /* check whether the overlay is safe to remove */
+        if (!overlay_removal_is_ok(ov)) {
+                err = -EBUSY;
+                pr_err("%s: removal check failed for overlay #%d\n",
+                                __func__, id);
+                goto out;
+        }
+
+
+        list_del(&ov->node);
+        of_changeset_revert(&ov->cset);
+        of_free_overlay_info(ov);
+        idr_remove(&ov_idr, id);
+        of_changeset_destroy(&ov->cset);
+        kfree(ov);
+
+        err = 0;
+
+out:
+        mutex_unlock(&of_mutex);
+
+        return err;
+}
+EXPORT_SYMBOL_GPL(of_overlay_destroy);
+
+/**
+ * of_overlay_destroy_all() - Removes all overlays from the system
+ *
+ * Removes all overlays from the system in the correct order.
+ *
+ * Returns 0 on success, or an negative error number
+ */
+int of_overlay_destroy_all(void)
+{
+        struct of_overlay *ov, *ovn;
+
+        mutex_lock(&of_mutex);
+
+        /* the tail of list is guaranteed to be safe to remove */
+        list_for_each_entry_safe_reverse(ov, ovn, &ov_list, node) {
+                list_del(&ov->node);
+                of_changeset_revert(&ov->cset);
+                of_free_overlay_info(ov);
+                idr_remove(&ov_idr, ov->id);
+                kfree(ov);
+        }
+
+        mutex_unlock(&of_mutex);
+
+        return 0;
+}
+EXPORT_SYMBOL_GPL(of_overlay_destroy_all);
diff --git a/include/linux/of.h b/include/linux/of.h
index fe1dec87fd68..aa01cf5852f8 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/list.h>
 
 #include <asm/byteorder.h>
 #include <asm/errno.h>
@@ -957,4 +958,34 @@ static inline int of_reconfig_get_state_change(unsigned long action,
 /* CONFIG_OF_RESOLVE api */
 extern int of_resolve_phandles(struct device_node *tree);
 
+/**
+ * Overlay support
+ */
+
+#ifdef CONFIG_OF_OVERLAY
+
+/* ID based overlays; the API for external users */
+int of_overlay_create(struct device_node *tree);
+int of_overlay_destroy(int id);
+int of_overlay_destroy_all(void);
+
+#else
+
+static inline int of_overlay_create(struct device_node *tree)
+{
+        return -ENOTSUPP;
+}
+
+static inline int of_overlay_destroy(int id)
+{
+        return -ENOTSUPP;
+}
+
+static inline int of_overlay_destroy_all(void)
+{
+        return -ENOTSUPP;
+}
+
+#endif
+
 #endif /* _LINUX_OF_H */