[PATCH v2 2/5] of: Support hashtable lookups for phandles

[Pantelis Antoniou]

When a device tree contains a lot of phandles, resolving one
takes time because the original method uses a search against
all nodes (not just the ones with phandles).

Signed-off-by: Pantelis Antoniou <pantelis.antoniou@xxxxxxxxxxxx>
---
 drivers/of/base.c       | 41 ++++++++++++++++++++++++++++++++++++++---
 drivers/of/dynamic.c    |  8 ++++++++
 drivers/of/of_private.h | 33 +++++++++++++++++++++++++++++++++
 include/linux/of.h      |  2 ++
 4 files changed, 81 insertions(+), 3 deletions(-)

diff --git a/drivers/of/base.c b/drivers/of/base.c
index 20bbc2f..436a088 100644
--- a/drivers/of/base.c
+++ b/drivers/of/base.c
@@ -27,6 +27,7 @@
 #include <linux/slab.h>
 #include <linux/string.h>
 #include <linux/proc_fs.h>
+#include <linux/rhashtable.h>
 
 #include "of_private.h"
 
@@ -41,6 +42,18 @@ static const char *of_stdout_options;
 
 struct kset *of_kset;
 
+const struct rhashtable_params of_phandle_ht_params = {
+	.key_offset = offsetof(struct device_node, phandle), /* base offset */
+	.key_len = sizeof(phandle),
+	.head_offset = offsetof(struct device_node, ht_node),
+	.automatic_shrinking = true,
+};
+
+struct rhashtable *of_phandle_ht;
+
+/* default is false */
+bool of_phandle_ht_is_disabled;
+
 /*
  * Used to protect the of_aliases, to hold off addition of nodes to sysfs.
  * This mutex must be held whenever modifications are being made to the
@@ -162,6 +175,12 @@ int __of_attach_node_post(struct device_node *np)
 	struct property *pp;
 	int rc;
 
+	if (of_phandle_ht_available()) {
+		rc = of_phandle_ht_insert(np);
+		WARN(rc, "insert to phandle hash fail @%s\n",
+				of_node_full_name(np));
+	}
+
 	if (!IS_ENABLED(CONFIG_SYSFS))
 		return 0;
 
@@ -194,6 +213,17 @@ void __init of_core_init(void)
 	struct device_node *np;
 	int ret;
 
+	of_phandle_ht = kzalloc(sizeof(*of_phandle_ht), GFP_KERNEL);
+	if (!of_phandle_ht) {
+		pr_warn("devicetree: Failed to allocate hashtable\n");
+		return;
+	}
+	ret = rhashtable_init(of_phandle_ht, &of_phandle_ht_params);
+	if (ret) {
+		pr_warn("devicetree: Failed to initialize hashtable\n");
+		return;
+	}
+
 	/* Create the kset, and register existing nodes */
 	mutex_lock(&of_mutex);
 	of_kset = kset_create_and_add("devicetree", NULL, firmware_kobj);
@@ -1073,9 +1103,14 @@ struct device_node *of_find_node_by_phandle(phandle handle)
 		return NULL;
 
 	raw_spin_lock_irqsave(&devtree_lock, flags);
-	for_each_of_allnodes(np)
-		if (np->phandle == handle)
-			break;
+	/* when we're ready use the hash table (and not disabled) */
+	if (of_phandle_ht_available() && !of_phandle_ht_is_disabled)
+		np = of_phandle_ht_lookup(handle);
+	else { /* fallback */
+		for_each_of_allnodes(np)
+			if (np->phandle == handle)
+				break;
+	}
 	of_node_get(np);
 	raw_spin_unlock_irqrestore(&devtree_lock, flags);
 	return np;
diff --git a/drivers/of/dynamic.c b/drivers/of/dynamic.c
index 34ca783..931b905 100644
--- a/drivers/of/dynamic.c
+++ b/drivers/of/dynamic.c
@@ -11,6 +11,7 @@
 #include <linux/slab.h>
 #include <linux/string.h>
 #include <linux/proc_fs.h>
+#include <linux/rhashtable.h>
 
 #include "of_private.h"
 
@@ -44,6 +45,13 @@ EXPORT_SYMBOL(of_node_put);
 void __of_detach_node_post(struct device_node *np)
 {
 	struct property *pp;
+	int rc;
+
+	if (of_phandle_ht_available()) {
+		rc = of_phandle_ht_remove(np);
+		WARN(rc, "remove from phandle hash fail @%s\n",
+				of_node_full_name(np));
+	}
 
 	if (!IS_ENABLED(CONFIG_SYSFS))
 		return;
diff --git a/drivers/of/of_private.h b/drivers/of/of_private.h
index 10b0342..386ae71 100644
--- a/drivers/of/of_private.h
+++ b/drivers/of/of_private.h
@@ -101,4 +101,37 @@ static inline int of_overlay_init(void)
 }
 #endif
 
+extern const struct rhashtable_params of_phandle_ht_params;
+extern struct rhashtable *of_phandle_ht;
+
+/* for unittest use */
+extern bool of_phandle_ht_is_disabled;
+
+static inline bool of_phandle_ht_available(void)
+{
+	return of_phandle_ht != NULL;
+}
+
+static inline int of_phandle_ht_insert(struct device_node *np)
+{
+	if (!np || !np->phandle)
+		return 0;
+	return rhashtable_insert_fast(of_phandle_ht,
+		&np->ht_node, of_phandle_ht_params);
+}
+
+static inline int of_phandle_ht_remove(struct device_node *np)
+{
+	if (!np || !np->phandle)
+		return 0;
+	return rhashtable_remove_fast(of_phandle_ht,
+		&np->ht_node, of_phandle_ht_params);
+}
+
+static inline struct device_node *of_phandle_ht_lookup(phandle handle)
+{
+	return rhashtable_lookup_fast(of_phandle_ht,
+			&handle, of_phandle_ht_params);
+}
+
 #endif /* _LINUX_OF_PRIVATE_H */
diff --git a/include/linux/of.h b/include/linux/of.h
index 18a8e59..9de9a3f 100644
--- a/include/linux/of.h
+++ b/include/linux/of.h
@@ -25,6 +25,7 @@
 #include <linux/notifier.h>
 #include <linux/property.h>
 #include <linux/list.h>
+#include <linux/rhashtable.h>
 
 #include <asm/byteorder.h>
 #include <asm/errno.h>
@@ -52,6 +53,7 @@ struct device_node {
 	phandle phandle;
 	const char *full_name;
 	struct fwnode_handle fwnode;
+	struct rhash_head ht_node;
 
 	struct	property *properties;
 	struct	property *deadprops;	/* removed properties */
-- 
1.7.12