regulator: Add helpers for low-level register access

Add helper functions that allow regulator consumers to obtain low-level
details about the regulator hardware, like the voltage selector register
address and such. These details can be useful when configuring hardware
or firmware that want to do low-level access to regulators, with no
involvement from the kernel.

The use-case for Tegra is a voltage-controlled oscillator clocksource
which has control logic to change the supply voltage via I2C to achieve
a desired output clock rate.

Signed-off-by: Tuomas Tynkkynen <ttynkkynen@nvidia.com>
Signed-off-by: Mark Brown <broonie@linaro.org>

include/linux/regulator/consumer.h

@@ -37,6 +37,7 @@
 
 struct device;
 struct notifier_block;
+struct regmap;
 
 /*
  * Regulator operating modes.
@@ -215,6 +216,13 @@ int regulator_set_optimum_mode(struct regulator *regulator, int load_uA);
 
 int regulator_allow_bypass(struct regulator *regulator, bool allow);
 
+struct regmap *regulator_get_regmap(struct regulator *regulator);
+int regulator_get_hardware_vsel_register(struct regulator *regulator,
+					 unsigned *vsel_reg,
+					 unsigned *vsel_mask);
+int regulator_list_hardware_vsel(struct regulator *regulator,
+				 unsigned selector);
+
 /* regulator notifier block */
 int regulator_register_notifier(struct regulator *regulator,
 			      struct notifier_block *nb);
@@ -452,6 +460,24 @@ static inline int regulator_allow_bypass(struct regulator *regulator,
 	return 0;
 }
 
+struct regmap *regulator_get_regmap(struct regulator *regulator)
+{
+	return ERR_PTR(-EOPNOTSUPP);
+}
+
+int regulator_get_hardware_vsel_register(struct regulator *regulator,
+					 unsigned *vsel_reg,
+					 unsigned *vsel_mask)
+{
+	return -EOPNOTSUPP;
+}
+
+int regulator_list_hardware_vsel(struct regulator *regulator,
+				 unsigned selector)
+{
+	return -EOPNOTSUPP;
+}
+
 static inline int regulator_register_notifier(struct regulator *regulator,
 			      struct notifier_block *nb)
 {