clk: adds support for transition-clock property

The transition-clock property defines a parent clock to be used by
a clock consumer during frequency transitions in variable frequency
clocks. It is specified by referencing a clock (must be a parent clock).

The clock functions clk_set_transition_parent and clk_get_transition_parent
are defined to work with the transition parent in clocks.

The clock function clk_use_transition_mode sets the clock parent to
the specified transition parent.

Signed-off-by: Octav Zlatior <octav.zlatior@theobroma-systems.com>

3 files changed, 96 insertions, 3 deletions

diff --git a/drivers/clk/clk.c b/drivers/clk/clk.c
index b59c1b4e80b1..421dfb4e8422 100644
--- a/drivers/clk/clk.c
+++ b/drivers/clk/clk.c
@@ -54,6 +54,7 @@ struct clk_core {
 	struct clk_core		*parent;
 	const char		**parent_names;
 	struct clk_core		**parents;
+	struct clk_core	*transition_parent;
 	u8			num_parents;
 	u8			new_parent_index;
 	unsigned long		rate;
@@ -1501,6 +1502,23 @@ static int __clk_set_parent(struct clk_core *clk, struct clk_core *parent,
 	return 0;
 }
 
+static struct clk *__clk_get_transition_parent(struct clk_core *clk) {
+	if (clk->transition_parent == NULL)
+		return NULL;
+	return clk->transition_parent->hw->clk;
+}
+
+static int __clk_set_transition_parent(struct clk_core *clk,
+	struct clk_core *parent)
+{
+	if (!clk)
+		return -EINVAL;
+
+	clk->transition_parent = parent;
+
+	return 0;
+}
+
 /**
  * __clk_speculate_rates
  * @clk: first clk in the subtree
@@ -2204,6 +2222,34 @@ bool clk_is_match(const struct clk *p, const struct clk *q)
 }
 EXPORT_SYMBOL_GPL(clk_is_match);
 
+struct clk* clk_get_transition_parent(struct clk *clk) {
+	if (!clk)
+		return NULL;
+
+	return __clk_get_transition_parent(clk->core);
+}
+EXPORT_SYMBOL_GPL(clk_get_transition_parent);
+
+int clk_set_transition_parent(struct clk *clk, struct clk *parent) {
+	if (!clk)
+		return -EINVAL;
+	if (!clk->core)
+		return -EINVAL;
+
+	return __clk_set_transition_parent(clk->core, parent->core);
+}
+EXPORT_SYMBOL_GPL(clk_set_transition_parent);
+
+int clk_use_transition_mode(struct clk *clk) {
+	if (!clk || !clk->core)
+		return -EINVAL;
+	if (clk->core->transition_parent == NULL)
+		return -EINVAL;
+
+	return clk_core_set_parent(clk->core, clk->core->transition_parent);
+}
+EXPORT_SYMBOL_GPL(clk_use_transition_mode);
+
 /**
  * __clk_init - initialize the data structures in a struct clk
  * @dev:	device initializing this clk, placeholder for now
@@ -2312,6 +2358,11 @@ static int __clk_init(struct device *dev, struct clk *clk_user)
 		hlist_add_head(&clk->child_node, &clk_orphan_list);
 
 	/*
+	 * Set the default transition parent to NULL (not used)
+	 */
+	clk->transition_parent = NULL;
+
+	/*
 	 * Set clk's accuracy.  The preferred method is to use
 	 * .recalc_accuracy. For simple clocks and lazy developers the default
 	 * fallback is to use the parent's accuracy.  If a clock doesn't have a
@@ -3093,7 +3144,6 @@ void __init of_clk_init(const struct of_device_id *matches)
 		list_for_each_entry_safe(clk_provider, next,
 					&clk_provider_list, node) {
 			if (force || parent_ready(clk_provider->np)) {
-
 				clk_provider->clk_init_cb(clk_provider->np);
 				of_clk_set_defaults(clk_provider->np, true);
 
diff --git a/drivers/clk/clkdev.c b/drivers/clk/clkdev.c
index 043fd3633373..5feaed862d0a 100644
--- a/drivers/clk/clkdev.c
+++ b/drivers/clk/clkdev.c
@@ -59,8 +59,9 @@ struct clk *of_clk_get_by_clkspec(struct of_phandle_args *clkspec)
 static struct clk *__of_clk_get(struct device_node *np, int index,
 			       const char *dev_id, const char *con_id)
 {
-	struct of_phandle_args clkspec;
-	struct clk *clk;
+	struct of_phandle_args clkspec, transition_clkspec;
+	struct clk *clk, *transition_clock;
+	struct device_node *clock_node;
 	int rc;
 
 	if (index < 0)
@@ -74,6 +75,21 @@ static struct clk *__of_clk_get(struct device_node *np, int index,
 	clk = __of_clk_get_by_clkspec(&clkspec, dev_id, con_id);
 	of_node_put(clkspec.np);
 
+	clock_node = of_parse_phandle(np, "clocks", 0);
+	of_node_put(clock_node);
+
+	if (clock_node != NULL) {
+		rc = of_parse_phandle_with_args(clock_node, "transition-clock", NULL,
+			0, &transition_clkspec);
+		of_node_put(transition_clkspec.np);
+
+		if (!rc) {
+			transition_clock = __of_clk_get_by_clkspec(&transition_clkspec,
+				dev_id, con_id);
+			clk_set_transition_parent(clk, transition_clock);
+		}
+	}
+
 	return clk;
 }
 
diff --git a/include/linux/clk.h b/include/linux/clk.h
index 68c16a6bedb3..4c2add0b4819 100644
--- a/include/linux/clk.h
+++ b/include/linux/clk.h
@@ -378,6 +378,33 @@ int clk_set_parent(struct clk *clk, struct clk *parent);
 struct clk *clk_get_parent(struct clk *clk);
 
 /**
+ * clk_get_transition_parent - return the transition parent to be used by
+ * a clock
+ * @clk: clock to get transition parent for
+ *
+ * Returns a pointer to the transition parent or NULL if not set
+ */
+struct clk *clk_get_transition_parent(struct clk *clk);
+
+/**
+ * clk_set_transition_parent - set the transition parent to be used by
+ * a clock
+ * @clk: clock to set transition parent for
+ * @parent: clock parent to set as transition parent
+ *
+ * Returns 0 on success or an error code otherwise
+ */
+int clk_set_transition_parent(struct clk *clk, struct clk *parent);
+
+/**
+ * clk_use_transition_mode - set the clock to "transition_mode"
+ * In transition mode, the clock will use the transition parent as parent
+ *
+ * Returns 0 on success or an error code otherwise
+ */
+int clk_use_transition_mode(struct clk *clk);
+
+/**
  * clk_get_sys - get a clock based upon the device name
  * @dev_id: device name
  * @con_id: connection ID