regulator: fixed: add support for ACPI interface

Add support to retrieve fixed voltage configure information through
ACPI interface. This is needed for Intel Bay Trail devices, where a
GPIO is used to control the USB vbus.
Signed-off-by: Lu Baolu <baolu.lu@linux.intel.com>
Signed-off-by: Mark Brown <broonie@kernel.org>

drivers/regulator/fixed.c

@@ -30,6 +30,9 @@
 #include <linux/of_gpio.h>
 #include <linux/regulator/of_regulator.h>
 #include <linux/regulator/machine.h>
+#include <linux/acpi.h>
+#include <linux/property.h>
+#include <linux/gpio/consumer.h>
 
 struct fixed_voltage_data {
 	struct regulator_desc desc;
@@ -94,6 +97,44 @@ of_get_fixed_voltage_config(struct device *dev,
 	return config;
 }
 
+/**
+ * acpi_get_fixed_voltage_config - extract fixed_voltage_config structure info
+ * @dev: device requesting for fixed_voltage_config
+ * @desc: regulator description
+ *
+ * Populates fixed_voltage_config structure by extracting data through ACPI
+ * interface, returns a pointer to the populated structure of NULL if memory
+ * alloc fails.
+ */
+static struct fixed_voltage_config *
+acpi_get_fixed_voltage_config(struct device *dev,
+			      const struct regulator_desc *desc)
+{
+	struct fixed_voltage_config *config;
+	const char *supply_name;
+	struct gpio_desc *gpiod;
+	int ret;
+
+	config = devm_kzalloc(dev, sizeof(*config), GFP_KERNEL);
+	if (!config)
+		return ERR_PTR(-ENOMEM);
+
+	ret = device_property_read_string(dev, "supply-name", &supply_name);
+	if (!ret)
+		config->supply_name = supply_name;
+
+	gpiod = gpiod_get(dev, "gpio", GPIOD_ASIS);
+	if (IS_ERR(gpiod))
+		return ERR_PTR(-ENODEV);
+
+	config->gpio = desc_to_gpio(gpiod);
+	config->enable_high = device_property_read_bool(dev,
+							"enable-active-high");
+	gpiod_put(gpiod);
+
+	return config;
+}
+
 static struct regulator_ops fixed_voltage_ops = {
 };
 
@@ -114,6 +155,11 @@ static int reg_fixed_voltage_probe(struct platform_device *pdev)
 						     &drvdata->desc);
 		if (IS_ERR(config))
 			return PTR_ERR(config);
+	} else if (ACPI_HANDLE(&pdev->dev)) {
+		config = acpi_get_fixed_voltage_config(&pdev->dev,
+						       &drvdata->desc);
+		if (IS_ERR(config))
+			return PTR_ERR(config);
 	} else {
 		config = dev_get_platdata(&pdev->dev);
 	}