[RFC/PATCH 2/4] clk: Make __clk_lookup() use a list instead of tree search

Stephen Boyd
2014-04-25T22:45:22Z

In the near future we're going to move the prepare lock to be a
per-clock ww_mutex. __clk_lookup() is called very deep in the
set-rate path and we would like to avoid having to take all the
locks in the clock tree to search for a clock (basically
defeating the purpose of introducing per-clock locks). Introduce
a new list that contains all clocks registered in the system and
walk this list until the clock is found.

Signed-off-by: Stephen Boyd <sboyd@codeaurora.org>
---
drivers/clk/clk.c | 52 +++++++++++++++++----------------------------
include/linux/clk-private.h | 1 +
2 files changed, 21 insertions(+), 32 deletions(-)

diff --git a/drivers/clk/clk.c b/drivers/clk/clk.c
index bebeaeec4aa1..fd22a4583013 100644
--- a/drivers/clk/clk.c
+++ b/drivers/clk/clk.c
@@ -32,8 +32,10 @@ static struct task_struct *enable_owner;
static int prepare_refcnt;
static int enable_refcnt;

+static DEFINE_MUTEX(clk_lookup_lock);
static HLIST_HEAD(clk_root_list);
static HLIST_HEAD(clk_orphan_list);
+static HLIST_HEAD(clk_lookup_list);
static LIST_HEAD(clk_notifier_list);

/*** locking ***/
@@ -706,46 +708,23 @@ out:
}
EXPORT_SYMBOL_GPL(__clk_is_enabled);

-static struct clk *__clk_lookup_subtree(const char *name, struct clk *clk)
-{
- struct clk *child;
- struct clk *ret;
-
- if (!strcmp(clk->name, name))
- return clk;
-
- hlist_for_each_entry(child, &clk->children, child_node) {
- ret = __clk_lookup_subtree(name, child);
- if (ret)
- return ret;
- }
-
- return NULL;
-}
-
struct clk *__clk_lookup(const char *name)
{
- struct clk *root_clk;
- struct clk *ret;
+ struct clk *clk;

if (!name)
return NULL;

- /* search the 'proper' clk tree first */
- hlist_for_each_entry(root_clk, &clk_root_list, child_node) {
- ret = __clk_lookup_subtree(name, root_clk);
- if (ret)
- return ret;
+ mutex_lock(&clk_lookup_lock);
+ hlist_for_each_entry(clk, &clk_lookup_list, lookup_node) {
+ if (!strcmp(clk->name, name))
+ goto found;
}
+ clk = NULL;
+found:
+ mutex_unlock(&clk_lookup_lock);

- /* if not found, then search the orphan tree */
- hlist_for_each_entry(root_clk, &clk_orphan_list, child_node) {
- ret = __clk_lookup_subtree(name, root_clk);
- if (ret)
- return ret;
- }
-
- return NULL;
+ return clk;
}

/*
@@ -1855,6 +1834,11 @@ int __clk_init(struct device *dev, struct clk *clk)

clk->parent = __clk_init_parent(clk);

+ /* Insert into clock lookup list */
+ mutex_lock(&clk_lookup_lock);
+ hlist_add_head(&clk->lookup_node, &clk_lookup_list);
+ mutex_unlock(&clk_lookup_lock);
+
/*
* Populate clk->parent if parent has already been __clk_init'd. If
* parent has not yet been __clk_init'd then place clk in the orphan
@@ -2159,6 +2143,10 @@ void clk_unregister(struct clk *clk)

hlist_del_init(&clk->child_node);

+ mutex_lock(&clk_lookup_lock);
+ hlist_del_init(&clk->lookup_node);
+ mutex_unlock(&clk_lookup_lock);
+
if (clk->prepare_count)
pr_warn("%s: unregistering prepared clock: %s\n",
__func__, clk->name);
diff --git a/include/linux/clk-private.h b/include/linux/clk-private.h
index efbf70b9fd84..3cd98a930006 100644
--- a/include/linux/clk-private.h
+++ b/include/linux/clk-private.h
@@ -48,6 +48,7 @@ struct clk {
unsigned long accuracy;
struct hlist_head children;
struct hlist_node child_node;
+ struct hlist_node lookup_node;
unsigned int notifier_count;
#ifdef CONFIG_DEBUG_FS
struct dentry *dentry;