regulator: core: Add core support for GPIO controlled enable lines

It is very common for regulators to support having their enable signal
controlled by a GPIO. Since there are a bunch of fiddly things to get
right like handling the operations when the enable signal is tied to
a rail and it's just replicated code add support for this to the core.

Drivers should set ena_gpio in their config if they have a GPIO control,
using ena_gpio_flags to specify any flags (including GPIOF_OUT_INIT_ for
the initial state) and ena_gpio_invert if the GPIO is active low. The
core will then override any enable and disable operations the driver has
and instead control the specified GPIO.

This will in the future also allow us to further extend the core by
identifying when several enable signals have been tied together and
handling this properly.
Signed-off-by: Mark Brown <broonie@opensource.wolfsonmicro.com>

drivers/regulator/core.c

@@ -23,6 +23,7 @@
 #include <linux/mutex.h>
 #include <linux/suspend.h>
 #include <linux/delay.h>
+#include <linux/gpio.h>
 #include <linux/of.h>
 #include <linux/regmap.h>
 #include <linux/regulator/of_regulator.h>
@@ -1491,7 +1492,11 @@ static int _regulator_do_enable(struct regulator_dev *rdev)
 
 	trace_regulator_enable(rdev_get_name(rdev));
 
-	if (rdev->desc->ops->enable) {
+	if (rdev->ena_gpio) {
+		gpio_set_value_cansleep(rdev->ena_gpio,
+					!rdev->ena_gpio_invert);
+		rdev->ena_gpio_state = 1;
+	} else if (rdev->desc->ops->enable) {
 		ret = rdev->desc->ops->enable(rdev);
 		if (ret < 0)
 			return ret;
@@ -1846,6 +1851,10 @@ EXPORT_SYMBOL_GPL(regulator_disable_regmap);
 
 static int _regulator_is_enabled(struct regulator_dev *rdev)
 {
+	/* A GPIO control always takes precedence */
+	if (rdev->ena_gpio)
+		return rdev->ena_gpio_state;
+
 	/* If we don't know then assume that the regulator is always on */
 	if (!rdev->desc->ops->is_enabled)
 		return 1;
@@ -3243,6 +3252,26 @@ regulator_register(const struct regulator_desc *regulator_desc,
 
 	dev_set_drvdata(&rdev->dev, rdev);
 
+	if (config->ena_gpio) {
+		ret = gpio_request_one(config->ena_gpio,
+				       GPIOF_DIR_OUT | config->ena_gpio_flags,
+				       rdev_get_name(rdev));
+		if (ret != 0) {
+			rdev_err(rdev, "Failed to request enable GPIO%d: %d\n",
+				 config->ena_gpio, ret);
+			goto clean;
+		}
+
+		rdev->ena_gpio = config->ena_gpio;
+		rdev->ena_gpio_invert = config->ena_gpio_invert;
+
+		if (config->ena_gpio_flags & GPIOF_OUT_INIT_HIGH)
+			rdev->ena_gpio_state = 1;
+
+		if (rdev->ena_gpio_invert)
+			rdev->ena_gpio_state = !rdev->ena_gpio_state;
+	}
+
 	/* set regulator constraints */
 	if (init_data)
 		constraints = &init_data->constraints;
@@ -3311,6 +3340,8 @@ regulator_register(const struct regulator_desc *regulator_desc,
 scrub:
 	if (rdev->supply)
 		regulator_put(rdev->supply);
+	if (rdev->ena_gpio)
+		gpio_free(rdev->ena_gpio);
 	kfree(rdev->constraints);
 	device_unregister(&rdev->dev);
 	/* device core frees rdev */
@@ -3344,6 +3375,8 @@ void regulator_unregister(struct regulator_dev *rdev)
 	unset_regulator_supplies(rdev);
 	list_del(&rdev->list);
 	kfree(rdev->constraints);
+	if (rdev->ena_gpio)
+		gpio_free(rdev->ena_gpio);
 	device_unregister(&rdev->dev);
 	mutex_unlock(&regulator_list_mutex);
 }

include/linux/regulator/driver.h

@@ -220,6 +220,9 @@ struct regulator_desc {
  * @of_node: OpenFirmware node to parse for device tree bindings (may be
  *           NULL).
  * @regmap: regmap to use for core regmap helpers
+ * @ena_gpio: GPIO controlling regulator enable.
+ * @ena_gpio_invert: Sense for GPIO enable control.
+ * @ena_gpio_flags: Flags to use when calling gpio_request_one()
  */
 struct regulator_config {
 	struct device *dev;
@@ -227,6 +230,10 @@ struct regulator_config {
 	void *driver_data;
 	struct device_node *of_node;
 	struct regmap *regmap;
+
+	int ena_gpio;
+	unsigned int ena_gpio_invert:1;
+	unsigned int ena_gpio_flags;
 };
 
 /*
@@ -265,6 +272,10 @@ struct regulator_dev {
 	void *reg_data;		/* regulator_dev data */
 
 	struct dentry *debugfs;
+
+	int ena_gpio;
+	unsigned int ena_gpio_invert:1;
+	unsigned int ena_gpio_state:1;
 };
 
 struct regulator_dev *