of: Transactional DT support.

Introducing DT transactional support.

A DT transaction is a method which allows one to apply changes
in the live tree, in such a way that either the full set of changes
take effect, or the state of the tree can be rolled-back to the
state it was before it was attempted. An applied transaction
can be rolled-back at any time.

Documentation is in
Documentation/devicetree/changesets.txt

Signed-off-by: Pantelis Antoniou <[e-mail]>
[glikely: Removed device notifiers and reworked to be more consistent]
Signed-off-by: Grant Likely <[e-mail]>

Documentation/devicetree/changesets.txt

···
+A DT changeset is a method which allows one to apply changes
+in the live tree in such a way that either the full set of changes
+will be applied, or none of them will be. If an error occurs partway
+through applying the changeset, then the tree will be rolled back to the
+previous state. A changeset can also be removed after it has been
+applied.
+
+When a changeset is applied, all of the changes get applied to the tree
+at once before emitting OF_RECONFIG notifiers. This is so that the
+receiver sees a complete and consistent state of the tree when it
+receives the notifier.
+
+The sequence of a changeset is as follows.
+
+1. of_changeset_init() - initializes a changeset
+
+2. A number of DT tree change calls, of_changeset_attach_node(),
+of_changeset_detach_node(), of_changeset_add_property(),
+of_changeset_remove_property, of_changeset_update_property() to prepare
+a set of changes. No changes to the active tree are made at this point.
+All the change operations are recorded in the of_changeset 'entries'
+list.
+
+3. mutex_lock(of_mutex) - starts a changeset; The global of_mutex
+ensures there can only be one editor at a time.
+
+4. of_changeset_apply() - Apply the changes to the tree. Either the
+entire changeset will get applied, or if there is an error the tree will
+be restored to the previous state
+
+5. mutex_unlock(of_mutex) - All operations complete, release the mutex
+
+If a successfully applied changeset needs to be removed, it can be done
+with the following sequence.
+
+1. mutex_lock(of_mutex)
+
+2. of_changeset_revert()
+
+3. mutex_unlock(of_mutex)

drivers/of/dynamic.c

···
 	kfree(node);
 	return NULL;
 }
+
+static void __of_changeset_entry_destroy(struct of_changeset_entry *ce)
+{
+	of_node_put(ce->np);
+	list_del(&ce->node);
+	kfree(ce);
+}
+
+#ifdef DEBUG
+static void __of_changeset_entry_dump(struct of_changeset_entry *ce)
+{
+	switch (ce->action) {
+	case OF_RECONFIG_ADD_PROPERTY:
+		pr_debug("%p: %s %s/%s\n",
+			ce, "ADD_PROPERTY   ", ce->np->full_name,
+			ce->prop->name);
+		break;
+	case OF_RECONFIG_REMOVE_PROPERTY:
+		pr_debug("%p: %s %s/%s\n",
+			ce, "REMOVE_PROPERTY", ce->np->full_name,
+			ce->prop->name);
+		break;
+	case OF_RECONFIG_UPDATE_PROPERTY:
+		pr_debug("%p: %s %s/%s\n",
+			ce, "UPDATE_PROPERTY", ce->np->full_name,
+			ce->prop->name);
+		break;
+	case OF_RECONFIG_ATTACH_NODE:
+		pr_debug("%p: %s %s\n",
+			ce, "ATTACH_NODE    ", ce->np->full_name);
+		break;
+	case OF_RECONFIG_DETACH_NODE:
+		pr_debug("%p: %s %s\n",
+			ce, "DETACH_NODE    ", ce->np->full_name);
+		break;
+	}
+}
+#else
+static inline void __of_changeset_entry_dump(struct of_changeset_entry *ce)
+{
+	/* empty */
+}
+#endif
+
+static void __of_changeset_entry_invert(struct of_changeset_entry *ce,
+					  struct of_changeset_entry *rce)
+{
+	memcpy(rce, ce, sizeof(*rce));
+
+	switch (ce->action) {
+	case OF_RECONFIG_ATTACH_NODE:
+		rce->action = OF_RECONFIG_DETACH_NODE;
+		break;
+	case OF_RECONFIG_DETACH_NODE:
+		rce->action = OF_RECONFIG_ATTACH_NODE;
+		break;
+	case OF_RECONFIG_ADD_PROPERTY:
+		rce->action = OF_RECONFIG_REMOVE_PROPERTY;
+		break;
+	case OF_RECONFIG_REMOVE_PROPERTY:
+		rce->action = OF_RECONFIG_ADD_PROPERTY;
+		break;
+	case OF_RECONFIG_UPDATE_PROPERTY:
+		rce->old_prop = ce->prop;
+		rce->prop = ce->old_prop;
+		break;
+	}
+}
+
+static void __of_changeset_entry_notify(struct of_changeset_entry *ce, bool revert)
+{
+	struct of_changeset_entry ce_inverted;
+	int ret;
+
+	if (revert) {
+		__of_changeset_entry_invert(ce, &ce_inverted);
+		ce = &ce_inverted;
+	}
+
+	switch (ce->action) {
+	case OF_RECONFIG_ATTACH_NODE:
+	case OF_RECONFIG_DETACH_NODE:
+		ret = of_reconfig_notify(ce->action, ce->np);
+		break;
+	case OF_RECONFIG_ADD_PROPERTY:
+	case OF_RECONFIG_REMOVE_PROPERTY:
+	case OF_RECONFIG_UPDATE_PROPERTY:
+		ret = of_property_notify(ce->action, ce->np, ce->prop, ce->old_prop);
+		break;
+	default:
+		pr_err("%s: invalid devicetree changeset action: %i\n", __func__,
+			(int)ce->action);
+		return;
+	}
+
+	if (ret)
+		pr_err("%s: notifier error @%s\n", __func__, ce->np->full_name);
+}
+
+static int __of_changeset_entry_apply(struct of_changeset_entry *ce)
+{
+	struct property *old_prop, **propp;
+	unsigned long flags;
+	int ret = 0;
+
+	__of_changeset_entry_dump(ce);
+
+	raw_spin_lock_irqsave(&devtree_lock, flags);
+	switch (ce->action) {
+	case OF_RECONFIG_ATTACH_NODE:
+		__of_attach_node(ce->np);
+		break;
+	case OF_RECONFIG_DETACH_NODE:
+		__of_detach_node(ce->np);
+		break;
+	case OF_RECONFIG_ADD_PROPERTY:
+		/* If the property is in deadprops then it must be removed */
+		for (propp = &ce->np->deadprops; *propp; propp = &(*propp)->next) {
+			if (*propp == ce->prop) {
+				*propp = ce->prop->next;
+				ce->prop->next = NULL;
+				break;
+			}
+		}
+
+		ret = __of_add_property(ce->np, ce->prop);
+		if (ret) {
+			pr_err("%s: add_property failed @%s/%s\n",
+				__func__, ce->np->full_name,
+				ce->prop->name);
+			break;
+		}
+		break;
+	case OF_RECONFIG_REMOVE_PROPERTY:
+		ret = __of_remove_property(ce->np, ce->prop);
+		if (ret) {
+			pr_err("%s: remove_property failed @%s/%s\n",
+				__func__, ce->np->full_name,
+				ce->prop->name);
+			break;
+		}
+		break;
+
+	case OF_RECONFIG_UPDATE_PROPERTY:
+		/* If the property is in deadprops then it must be removed */
+		for (propp = &ce->np->deadprops; *propp; propp = &(*propp)->next) {
+			if (*propp == ce->prop) {
+				*propp = ce->prop->next;
+				ce->prop->next = NULL;
+				break;
+			}
+		}
+
+		ret = __of_update_property(ce->np, ce->prop, &old_prop);
+		if (ret) {
+			pr_err("%s: update_property failed @%s/%s\n",
+				__func__, ce->np->full_name,
+				ce->prop->name);
+			break;
+		}
+		break;
+	default:
+		ret = -EINVAL;
+	}
+	raw_spin_unlock_irqrestore(&devtree_lock, flags);
+
+	if (ret)
+		return ret;
+
+	switch (ce->action) {
+	case OF_RECONFIG_ATTACH_NODE:
+		__of_attach_node_sysfs(ce->np);
+		break;
+	case OF_RECONFIG_DETACH_NODE:
+		__of_detach_node_sysfs(ce->np);
+		break;
+	case OF_RECONFIG_ADD_PROPERTY:
+		/* ignore duplicate names */
+		__of_add_property_sysfs(ce->np, ce->prop);
+		break;
+	case OF_RECONFIG_REMOVE_PROPERTY:
+		__of_remove_property_sysfs(ce->np, ce->prop);
+		break;
+	case OF_RECONFIG_UPDATE_PROPERTY:
+		__of_update_property_sysfs(ce->np, ce->prop, ce->old_prop);
+		break;
+	}
+
+	return 0;
+}
+
+static inline int __of_changeset_entry_revert(struct of_changeset_entry *ce)
+{
+	struct of_changeset_entry ce_inverted;
+
+	__of_changeset_entry_invert(ce, &ce_inverted);
+	return __of_changeset_entry_apply(&ce_inverted);
+}
+
+/**
+ * of_changeset_init - Initialize a changeset for use
+ *
+ * @ocs:	changeset pointer
+ *
+ * Initialize a changeset structure
+ */
+void of_changeset_init(struct of_changeset *ocs)
+{
+	memset(ocs, 0, sizeof(*ocs));
+	INIT_LIST_HEAD(&ocs->entries);
+}
+
+/**
+ * of_changeset_destroy - Destroy a changeset
+ *
+ * @ocs:	changeset pointer
+ *
+ * Destroys a changeset. Note that if a changeset is applied,
+ * its changes to the tree cannot be reverted.
+ */
+void of_changeset_destroy(struct of_changeset *ocs)
+{
+	struct of_changeset_entry *ce, *cen;
+
+	list_for_each_entry_safe_reverse(ce, cen, &ocs->entries, node)
+		__of_changeset_entry_destroy(ce);
+}
+
+/**
+ * of_changeset_apply - Applies a changeset
+ *
+ * @ocs:	changeset pointer
+ *
+ * Applies a changeset to the live tree.
+ * Any side-effects of live tree state changes are applied here on
+ * sucess, like creation/destruction of devices and side-effects
+ * like creation of sysfs properties and directories.
+ * Returns 0 on success, a negative error value in case of an error.
+ * On error the partially applied effects are reverted.
+ */
+int of_changeset_apply(struct of_changeset *ocs)
+{
+	struct of_changeset_entry *ce;
+	int ret;
+
+	/* perform the rest of the work */
+	pr_debug("of_changeset: applying...\n");
+	list_for_each_entry(ce, &ocs->entries, node) {
+		ret = __of_changeset_entry_apply(ce);
+		if (ret) {
+			pr_err("%s: Error applying changeset (%d)\n", __func__, ret);
+			list_for_each_entry_continue_reverse(ce, &ocs->entries, node)
+				__of_changeset_entry_revert(ce);
+			return ret;
+		}
+	}
+	pr_debug("of_changeset: applied, emitting notifiers.\n");
+
+	/* drop the global lock while emitting notifiers */
+	mutex_unlock(&of_mutex);
+	list_for_each_entry(ce, &ocs->entries, node)
+		__of_changeset_entry_notify(ce, 0);
+	mutex_lock(&of_mutex);
+	pr_debug("of_changeset: notifiers sent.\n");
+
+	return 0;
+}
+
+/**
+ * of_changeset_revert - Reverts an applied changeset
+ *
+ * @ocs:	changeset pointer
+ *
+ * Reverts a changeset returning the state of the tree to what it
+ * was before the application.
+ * Any side-effects like creation/destruction of devices and
+ * removal of sysfs properties and directories are applied.
+ * Returns 0 on success, a negative error value in case of an error.
+ */
+int of_changeset_revert(struct of_changeset *ocs)
+{
+	struct of_changeset_entry *ce;
+	int ret;
+
+	pr_debug("of_changeset: reverting...\n");
+	list_for_each_entry_reverse(ce, &ocs->entries, node) {
+		ret = __of_changeset_entry_revert(ce);
+		if (ret) {
+			pr_err("%s: Error reverting changeset (%d)\n", __func__, ret);
+			list_for_each_entry_continue(ce, &ocs->entries, node)
+				__of_changeset_entry_apply(ce);
+			return ret;
+		}
+	}
+	pr_debug("of_changeset: reverted, emitting notifiers.\n");
+
+	/* drop the global lock while emitting notifiers */
+	mutex_unlock(&of_mutex);
+	list_for_each_entry_reverse(ce, &ocs->entries, node)
+		__of_changeset_entry_notify(ce, 1);
+	mutex_lock(&of_mutex);
+	pr_debug("of_changeset: notifiers sent.\n");
+
+	return 0;
+}
+
+/**
+ * of_changeset_action - Perform a changeset action
+ *
+ * @ocs:	changeset pointer
+ * @action:	action to perform
+ * @np:		Pointer to device node
+ * @prop:	Pointer to property
+ *
+ * On action being one of:
+ * + OF_RECONFIG_ATTACH_NODE
+ * + OF_RECONFIG_DETACH_NODE,
+ * + OF_RECONFIG_ADD_PROPERTY
+ * + OF_RECONFIG_REMOVE_PROPERTY,
+ * + OF_RECONFIG_UPDATE_PROPERTY
+ * Returns 0 on success, a negative error value in case of an error.
+ */
+int of_changeset_action(struct of_changeset *ocs, unsigned long action,
+		struct device_node *np, struct property *prop)
+{
+	struct of_changeset_entry *ce;
+
+	ce = kzalloc(sizeof(*ce), GFP_KERNEL);
+	if (!ce) {
+		pr_err("%s: Failed to allocate\n", __func__);
+		return -ENOMEM;
+	}
+	/* get a reference to the node */
+	ce->action = action;
+	ce->np = of_node_get(np);
+	ce->prop = prop;
+
+	if (action == OF_RECONFIG_UPDATE_PROPERTY && prop)
+		ce->old_prop = of_find_property(np, prop->name, NULL);
+
+	/* add it to the list */
+	list_add_tail(&ce->node, &ocs->entries);
+	return 0;
+}

drivers/of/of_private.h

···
 extern void __of_detach_node(struct device_node *np);
 extern void __of_detach_node_sysfs(struct device_node *np);
 
+/* iterators for transactions, used for overlays */
+/* forward iterator */
+#define for_each_transaction_entry(_oft, _te) \
+	list_for_each_entry(_te, &(_oft)->te_list, node)
+
+/* reverse iterator */
+#define for_each_transaction_entry_reverse(_oft, _te) \
+	list_for_each_entry_reverse(_te, &(_oft)->te_list, node)
+
 #endif /* _LINUX_OF_PRIVATE_H */

drivers/of/selftest.c

···
 #endif
 }
 
+static void __init of_selftest_changeset(void)
+{
+#ifdef CONFIG_OF_DYNAMIC
+	struct property *ppadd, padd = { .name = "prop-add", .length = 0, .value = "" };
+	struct property *ppupdate, pupdate = { .name = "prop-update", .length = 5, .value = "abcd" };
+	struct property *ppremove;
+	struct device_node *n1, *n2, *n21, *nremove, *parent;
+	struct of_changeset chgset;
+
+	of_changeset_init(&chgset);
+	n1 = __of_node_alloc("/testcase-data/changeset/n1", GFP_KERNEL);
+	selftest(n1, "testcase setup failure\n");
+	n2 = __of_node_alloc("/testcase-data/changeset/n2", GFP_KERNEL);
+	selftest(n2, "testcase setup failure\n");
+	n21 = __of_node_alloc("/testcase-data/changeset/n2/n21", GFP_KERNEL);
+	selftest(n21, "testcase setup failure %p\n", n21);
+	nremove = of_find_node_by_path("/testcase-data/changeset/node-remove");
+	selftest(nremove, "testcase setup failure\n");
+	ppadd = __of_prop_dup(&padd, GFP_KERNEL);
+	selftest(ppadd, "testcase setup failure\n");
+	ppupdate = __of_prop_dup(&pupdate, GFP_KERNEL);
+	selftest(ppupdate, "testcase setup failure\n");
+	parent = nremove->parent;
+	n1->parent = parent;
+	n2->parent = parent;
+	n21->parent = n2;
+	n2->child = n21;
+	ppremove = of_find_property(parent, "prop-remove", NULL);
+	selftest(ppremove, "failed to find removal prop");
+
+	of_changeset_init(&chgset);
+	selftest(!of_changeset_attach_node(&chgset, n1), "fail attach n1\n");
+	selftest(!of_changeset_attach_node(&chgset, n2), "fail attach n2\n");
+	selftest(!of_changeset_detach_node(&chgset, nremove), "fail remove node\n");
+	selftest(!of_changeset_attach_node(&chgset, n21), "fail attach n21\n");
+	selftest(!of_changeset_add_property(&chgset, parent, ppadd), "fail add prop\n");
+	selftest(!of_changeset_update_property(&chgset, parent, ppupdate), "fail update prop\n");
+	selftest(!of_changeset_remove_property(&chgset, parent, ppremove), "fail remove prop\n");
+	mutex_lock(&of_mutex);
+	selftest(!of_changeset_apply(&chgset), "apply failed\n");
+	mutex_unlock(&of_mutex);
+
+	mutex_lock(&of_mutex);
+	selftest(!of_changeset_revert(&chgset), "revert failed\n");
+	mutex_unlock(&of_mutex);
+
+	of_changeset_destroy(&chgset);
+#endif
+}
+
 static void __init of_selftest_parse_interrupts(void)
 {
 	struct device_node *np;
···
 	of_selftest_parse_phandle_with_args();
 	of_selftest_property_match_string();
 	of_selftest_property_copy();
+	of_selftest_changeset();
 	of_selftest_parse_interrupts();
 	of_selftest_parse_interrupts_extended();
 	of_selftest_match_node();

drivers/of/testcase-data/testcases.dtsi

···
+/ {
+	testcase-data {
+		changeset {
+			prop-update = "hello";
+			prop-remove = "world";
+			node-remove {
+			};
+		};
+	};
+};
 #include "tests-phandle.dtsi"
 #include "tests-interrupts.dtsi"
 #include "tests-match.dtsi"

include/linux/of.h

···
 #define OF_DECLARE_2(table, name, compat, fn) \
 		_OF_DECLARE(table, name, compat, fn, of_init_fn_2)
 
+/**
+ * struct of_changeset_entry	- Holds a changeset 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 a changeset
+ * is held in a list of of_changeset_entry structures.
+ * That way we can recover from a partial application, or we can
+ * revert the changeset
+ */
+struct of_changeset_entry {
+	struct list_head node;
+	unsigned long action;
+	struct device_node *np;
+	struct property *prop;
+	struct property *old_prop;
+};
+
+/**
+ * struct of_changeset - changeset tracker structure
+ *
+ * @entries:	list_head for the changeset entries
+ *
+ * changesets are a convenient way to apply bulk changes to the
+ * live tree. In case of an error, changes are rolled-back.
+ * changesets live on after initial application, and if not
+ * destroyed after use, they can be reverted in one single call.
+ */
+struct of_changeset {
+	struct list_head entries;
+};
+
+#ifdef CONFIG_OF_DYNAMIC
+extern void of_changeset_init(struct of_changeset *ocs);
+extern void of_changeset_destroy(struct of_changeset *ocs);
+extern int of_changeset_apply(struct of_changeset *ocs);
+extern int of_changeset_revert(struct of_changeset *ocs);
+extern int of_changeset_action(struct of_changeset *ocs,
+		unsigned long action, struct device_node *np,
+		struct property *prop);
+
+static inline int of_changeset_attach_node(struct of_changeset *ocs,
+		struct device_node *np)
+{
+	return of_changeset_action(ocs, OF_RECONFIG_ATTACH_NODE, np, NULL);
+}
+
+static inline int of_changeset_detach_node(struct of_changeset *ocs,
+		struct device_node *np)
+{
+	return of_changeset_action(ocs, OF_RECONFIG_DETACH_NODE, np, NULL);
+}
+
+static inline int of_changeset_add_property(struct of_changeset *ocs,
+		struct device_node *np, struct property *prop)
+{
+	return of_changeset_action(ocs, OF_RECONFIG_ADD_PROPERTY, np, prop);
+}
+
+static inline int of_changeset_remove_property(struct of_changeset *ocs,
+		struct device_node *np, struct property *prop)
+{
+	return of_changeset_action(ocs, OF_RECONFIG_REMOVE_PROPERTY, np, prop);
+}
+
+static inline int of_changeset_update_property(struct of_changeset *ocs,
+		struct device_node *np, struct property *prop)
+{
+	return of_changeset_action(ocs, OF_RECONFIG_UPDATE_PROPERTY, np, prop);
+}
+#endif
+
 #endif /* _LINUX_OF_H */