reset: Add optional resets and stubs

This patch adds device_reset_optional and (devm_)reset_control_get_optional
variants that drivers can use to indicate they can function without control
over the reset line. For those functions, stubs are added so the drivers can
be compiled with CONFIG_RESET_CONTROLLER disabled.
Also, device_reset is annotated with __must_check. Drivers ignoring the return
value should use device_reset_optional instead.
Signed-off-by: Philipp Zabel <p.zabel@pengutronix.de>
Reviewed-by: Maxime Ripard <maxime.ripard@free-electrons.com>
Reviewed-by: Marek Vasut <marex@denx.de>
Acked-by: Wolfram Sang <wsa@the-dreams.de>

include/linux/reset.h

 #ifndef _LINUX_RESET_H_
 #define _LINUX_RESET_H_
 
-#include <linux/of.h>
-
 struct device;
 struct reset_control;
 
+#ifdef CONFIG_RESET_CONTROLLER
+
 int reset_control_reset(struct reset_control *rstc);
 int reset_control_assert(struct reset_control *rstc);
 int reset_control_deassert(struct reset_control *rstc);
 
-struct reset_control *of_reset_control_get(struct device_node *node,
-					   const char *id);
 struct reset_control *reset_control_get(struct device *dev, const char *id);
 void reset_control_put(struct reset_control *rstc);
 struct reset_control *devm_reset_control_get(struct device *dev, const char *id);
 
-int device_reset(struct device *dev);
+int __must_check device_reset(struct device *dev);
+
+static inline int device_reset_optional(struct device *dev)
+{
+	return device_reset(dev);
+}
+
+static inline struct reset_control *reset_control_get_optional(
+					struct device *dev, const char *id)
+{
+	return reset_control_get(dev, id);
+}
+
+static inline struct reset_control *devm_reset_control_get_optional(
+					struct device *dev, const char *id)
+{
+	return devm_reset_control_get(dev, id);
+}
+
+#else
+
+static inline int reset_control_reset(struct reset_control *rstc)
+{
+	WARN_ON(1);
+	return 0;
+}
+
+static inline int reset_control_assert(struct reset_control *rstc)
+{
+	WARN_ON(1);
+	return 0;
+}
+
+static inline int reset_control_deassert(struct reset_control *rstc)
+{
+	WARN_ON(1);
+	return 0;
+}
+
+static inline void reset_control_put(struct reset_control *rstc)
+{
+	WARN_ON(1);
+}
+
+static inline int device_reset_optional(struct device *dev)
+{
+	return -ENOSYS;
+}
+
+static inline struct reset_control *reset_control_get_optional(
+					struct device *dev, const char *id)
+{
+	return ERR_PTR(-ENOSYS);
+}
+
+static inline struct reset_control *devm_reset_control_get_optional(
+					struct device *dev, const char *id)
+{
+	return ERR_PTR(-ENOSYS);
+}
+
+#endif /* CONFIG_RESET_CONTROLLER */
 
 #endif