reset: add reset_control_status helper function

There are cases where a system will want to read a reset status bit before
doing any other toggling. Add a reset_control_status helper function to the
reset controller API.

Signed-off-by: Dinh Nguyen <[e-mail]>
Signed-off-by: Philipp Zabel <[e-mail]>

drivers/reset/core.c

···
 EXPORT_SYMBOL_GPL(reset_control_deassert);
 
 /**
+ * reset_control_status - returns a negative errno if not supported, a
+ * positive value if the reset line is asserted, or zero if the reset
+ * line is not asserted.
+ * @rstc: reset controller
+ */
+int reset_control_status(struct reset_control *rstc)
+{
+	if (rstc->rcdev->ops->status)
+		return rstc->rcdev->ops->status(rstc->rcdev, rstc->id);
+
+	return -ENOSYS;
+}
+EXPORT_SYMBOL_GPL(reset_control_status);
+
+/**
  * of_reset_control_get - Lookup and obtain a reference to a reset controller.
  * @node: device to be reset by the controller
  * @id: reset line name

include/linux/reset-controller.h

···
  *         things to reset the device
  * @assert: manually assert the reset line, if supported
  * @deassert: manually deassert the reset line, if supported
+ * @status: return the status of the reset line, if supported
  */
 struct reset_control_ops {
 	int (*reset)(struct reset_controller_dev *rcdev, unsigned long id);
 	int (*assert)(struct reset_controller_dev *rcdev, unsigned long id);
 	int (*deassert)(struct reset_controller_dev *rcdev, unsigned long id);
+	int (*status)(struct reset_controller_dev *rcdev, unsigned long id);
 };
 
 struct module;

include/linux/reset.h

···
 int reset_control_reset(struct reset_control *rstc);
 int reset_control_assert(struct reset_control *rstc);
 int reset_control_deassert(struct reset_control *rstc);
+int reset_control_status(struct reset_control *rstc);
 
 struct reset_control *reset_control_get(struct device *dev, const char *id);
 void reset_control_put(struct reset_control *rstc);
···
 }
 
 static inline int reset_control_deassert(struct reset_control *rstc)
+{
+	WARN_ON(1);
+	return 0;
+}
+
+static inline int reset_control_status(struct reset_control *rstc)
 {
 	WARN_ON(1);
 	return 0;