regulator: Add support for ramp delay

Changing voltage and enabling regulator might require delays so the
regulator stabilizes at expected level.

Add support for "regulator-ramp-delay" binding which can introduce
required time to both enabling the regulator and to changing the
voltage.

Signed-off-by: Krzysztof Kozlowski <krzk@kernel.org>
Tested-by: Anand Moon <linux.amoon@gmail.com>
Signed-off-by: Minkyu Kang <mk7.kang@samsung.com>
diff --git a/include/power/regulator.h b/include/power/regulator.h
index 314160a..6c6e2cd 100644
--- a/include/power/regulator.h
+++ b/include/power/regulator.h
@@ -150,6 +150,7 @@
  * @always_on* - bool type, true or false
  * @boot_on*   - bool type, true or false
  * TODO(sjg@chromium.org): Consider putting the above two into @flags
+ * @ramp_delay - Time to settle down after voltage change (unit: uV/us)
  * @flags:     - flags value (see REGULATOR_FLAG_...)
  * @name**     - fdt regulator name - should be taken from the device tree
  * ctrl_reg:   - Control register offset used to enable/disable regulator
@@ -169,6 +170,7 @@
 	int max_uV;
 	int min_uA;
 	int max_uA;
+	unsigned int ramp_delay;
 	bool always_on;
 	bool boot_on;
 	const char *name;