clk: Add (devm_)clk_get_optional() functions

This adds clk_get_optional() and devm_clk_get_optional() functions to get
optional clocks.

They behave the same as (devm_)clk_get() except where there is no clock
producer. In this case, instead of returning -ENOENT, the function
returns NULL. This makes error checking simpler and allows
clk_prepare_enable, etc to be called on the returned reference
without additional checks.

Signed-off-by: Phil Edworthy <phil.edworthy@renesas.com>
Reviewed-by: Andy Shevchenko <andriy.shevchenko@linux.intel.com>
Cc: Russell King <linux@armlinux.org.uk>
[sboyd@kernel.org: Document in devres.txt]
Signed-off-by: Stephen Boyd <sboyd@kernel.org>

Documentation/driver-model/devres.txt

@@ -242,6 +242,7 @@ certainly invest a bit more effort into libata core layer).
 
 CLOCK
   devm_clk_get()
+  devm_clk_get_optional()
   devm_clk_put()
   devm_clk_hw_register()
   devm_of_clk_add_hw_provider()

drivers/clk/clk-devres.c

@@ -29,6 +29,17 @@ struct clk *devm_clk_get(struct device *dev, const char *id)
 }
 EXPORT_SYMBOL(devm_clk_get);
 
+struct clk *devm_clk_get_optional(struct device *dev, const char *id)
+{
+	struct clk *clk = devm_clk_get(dev, id);
+
+	if (clk == ERR_PTR(-ENOENT))
+		return NULL;
+
+	return clk;
+}
+EXPORT_SYMBOL(devm_clk_get_optional);
+
 struct clk_bulk_devres {
 	struct clk_bulk_data *clks;
 	int num_clks;

include/linux/clk.h

@@ -383,6 +383,17 @@ int __must_check devm_clk_bulk_get_all(struct device *dev,
  */
 struct clk *devm_clk_get(struct device *dev, const char *id);
 
+/**
+ * devm_clk_get_optional - lookup and obtain a managed reference to an optional
+ *			   clock producer.
+ * @dev: device for clock "consumer"
+ * @id: clock consumer ID
+ *
+ * Behaves the same as devm_clk_get() except where there is no clock producer.
+ * In this case, instead of returning -ENOENT, the function returns NULL.
+ */
+struct clk *devm_clk_get_optional(struct device *dev, const char *id);
+
 /**
  * devm_get_clk_from_child - lookup and obtain a managed reference to a
  *			     clock producer from child node.
@@ -718,6 +729,12 @@ static inline struct clk *devm_clk_get(struct device *dev, const char *id)
 	return NULL;
 }
 
+static inline struct clk *devm_clk_get_optional(struct device *dev,
+						const char *id)
+{
+	return NULL;
+}
+
 static inline int __must_check devm_clk_bulk_get(struct device *dev, int num_clks,
 						 struct clk_bulk_data *clks)
 {
@@ -862,6 +879,25 @@ static inline void clk_bulk_disable_unprepare(int num_clks,
 	clk_bulk_unprepare(num_clks, clks);
 }
 
+/**
+ * clk_get_optional - lookup and obtain a reference to an optional clock
+ *		      producer.
+ * @dev: device for clock "consumer"
+ * @id: clock consumer ID
+ *
+ * Behaves the same as clk_get() except where there is no clock producer. In
+ * this case, instead of returning -ENOENT, the function returns NULL.
+ */
+static inline struct clk *clk_get_optional(struct device *dev, const char *id)
+{
+	struct clk *clk = clk_get(dev, id);
+
+	if (clk == ERR_PTR(-ENOENT))
+		return NULL;
+
+	return clk;
+}
+
 #if defined(CONFIG_OF) && defined(CONFIG_COMMON_CLK)
 struct clk *of_clk_get(struct device_node *np, int index);
 struct clk *of_clk_get_by_name(struct device_node *np, const char *name);