regulator: gpio-regulator: Catch 'no states property' misuse

A selection of voltage or current values (AKA states) should always
be specified when using a GPIO regulator. If there are no switchable
states then the fixed regulators should be used instead.
Signed-off-by: Lee Jones <lee.jones@linaro.org>
Signed-off-by: Mark Brown <broonie@opensource.wolfsonmicro.com>

Documentation/devicetree/bindings/regulator/gpio-regulator.txt

@@ -2,11 +2,12 @@ GPIO controlled regulators
 
 Required properties:
 - compatible		: Must be "regulator-gpio".
+- states		: Selection of available voltages and GPIO configs.
+                          if there are no states, then use a fixed regulator
 
 Optional properties:
 - enable-gpio		: GPIO to use to enable/disable the regulator.
 - gpios			: GPIO group used to control voltage.
-- states		: Selection of available voltages and GPIO configs.
 - startup-delay-us	: Startup time in microseconds.
 - enable-active-high	: Polarity of GPIO is active high (default is low).
 

drivers/regulator/gpio-regulator.c

@@ -183,6 +183,11 @@ of_get_gpio_regulator_config(struct device *dev, struct device_node *np)
 
 	/* Fetch states. */
 	prop = of_find_property(np, "states", NULL);
+	if (!prop) {
+		dev_err(dev, "No 'states' property found\n");
+		return ERR_PTR(-EINVAL);
+	}
+
 	proplen = prop->length / sizeof(int);
 
 	config->states = devm_kzalloc(dev,