regulator: core: Support bypass mode

Many regulators support a bypass mode where they simply switch their
input supply to the output. This is mainly used in low power retention
states where power consumption is extremely low so higher voltage or
less clean supplies can be used.

Support this by providing ops for the drivers and a consumer API which
allows the device to be put into bypass mode if all consumers enable it
and the machine enables permission for this.

This is not supported as a mode since the existing modes are rarely used
due to fuzzy definition and mostly redundant with modern hardware which is
able to respond promptly to load changes.

Signed-off-by: Mark Brown <[e-mail]>
Reviewed-by: Graeme Gregory <[e-mail]>

Documentation/ABI/testing/sysfs-class-regulator

···
 
 		This will be one of the same strings reported by
 		the "state" attribute.
+
+What:		/sys/class/regulator/.../bypass
+Date:		September 2012
+KernelVersion:	3.7
+Contact:	Mark Brown <[e-mail]>
+Description:
+		Some regulator directories will contain a field called
+		bypass.  This indicates if the device is in bypass mode.
+
+		This will be one of the following strings:
+
+		'enabled'
+		'disabled'
+		'unknown'
+
+		'enabled' means the regulator is in bypass mode.
+
+		'disabled' means that the regulator is regulating.
+
+		'unknown' means software cannot determine the state, or
+		the reported state is invalid.

drivers/regulator/core.c

···
 	struct device *dev;
 	struct list_head list;
 	unsigned int always_on:1;
+	unsigned int bypass:1;
 	int uA_load;
 	int min_uV;
 	int max_uV;
···
 	case REGULATOR_STATUS_STANDBY:
 		label = "standby";
 		break;
+	case REGULATOR_STATUS_BYPASS:
+		label = "bypass";
+		break;
 	case REGULATOR_STATUS_UNDEFINED:
 		label = "undefined";
 		break;
···
 static DEVICE_ATTR(suspend_standby_state, 0444,
 		regulator_suspend_standby_state_show, NULL);
 
+static ssize_t regulator_bypass_show(struct device *dev,
+				     struct device_attribute *attr, char *buf)
+{
+	struct regulator_dev *rdev = dev_get_drvdata(dev);
+	const char *report;
+	bool bypass;
+	int ret;
+
+	ret = rdev->desc->ops->get_bypass(rdev, &bypass);
+
+	if (ret != 0)
+		report = "unknown";
+	else if (bypass)
+		report = "enabled";
+	else
+		report = "disabled";
+
+	return sprintf(buf, "%s\n", report);
+}
+static DEVICE_ATTR(bypass, 0444,
+		   regulator_bypass_show, NULL);
 
 /*
  * These are the only attributes are present for all regulators.
···
 EXPORT_SYMBOL_GPL(regulator_set_optimum_mode);
 
 /**
+ * regulator_allow_bypass - allow the regulator to go into bypass mode
+ *
+ * @regulator: Regulator to configure
+ * @allow: enable or disable bypass mode
+ *
+ * Allow the regulator to go into bypass mode if all other consumers
+ * for the regulator also enable bypass mode and the machine
+ * constraints allow this.  Bypass mode means that the regulator is
+ * simply passing the input directly to the output with no regulation.
+ */
+int regulator_allow_bypass(struct regulator *regulator, bool enable)
+{
+	struct regulator_dev *rdev = regulator->rdev;
+	int ret = 0;
+
+	if (!rdev->desc->ops->set_bypass)
+		return 0;
+
+	if (rdev->constraints &&
+	    !(rdev->constraints->valid_ops_mask & REGULATOR_CHANGE_BYPASS))
+		return 0;
+
+	mutex_lock(&rdev->mutex);
+
+	if (enable && !regulator->bypass) {
+		rdev->bypass_count++;
+
+		if (rdev->bypass_count == rdev->open_count) {
+			ret = rdev->desc->ops->set_bypass(rdev, enable);
+			if (ret != 0)
+				rdev->bypass_count--;
+		}
+
+	} else if (!enable && regulator->bypass) {
+		rdev->bypass_count--;
+
+		if (rdev->bypass_count != rdev->open_count) {
+			ret = rdev->desc->ops->set_bypass(rdev, enable);
+			if (ret != 0)
+				rdev->bypass_count++;
+		}
+	}
+
+	if (ret == 0)
+		regulator->bypass = enable;
+
+	mutex_unlock(&rdev->mutex);
+
+	return ret;
+}
+EXPORT_SYMBOL_GPL(regulator_allow_bypass);
+
+/**
  * regulator_register_notifier - register regulator event notifier
  * @regulator: regulator source
  * @nb: notifier block
···
 		if (status < 0)
 			return status;
 	}
+	if (ops->get_bypass) {
+		status = device_create_file(dev, &dev_attr_bypass);
+		if (status < 0)
+			return status;
+	}
 
 	/* some attributes are type-specific */
 	if (rdev->desc->type == REGULATOR_CURRENT) {
···
 			   &rdev->use_count);
 	debugfs_create_u32("open_count", 0444, rdev->debugfs,
 			   &rdev->open_count);
+	debugfs_create_u32("bypass_count", 0444, rdev->debugfs,
+			   &rdev->bypass_count);
 }
 
 /**

include/linux/regulator/consumer.h

···
 unsigned int regulator_get_mode(struct regulator *regulator);
 int regulator_set_optimum_mode(struct regulator *regulator, int load_uA);
 
+int regulator_allow_bypass(struct regulator *regulator, bool allow);
+
 /* regulator notifier block */
 int regulator_register_notifier(struct regulator *regulator,
 			      struct notifier_block *nb);
···
 					int load_uA)
 {
 	return REGULATOR_MODE_NORMAL;
+}
+
+static inline int regulator_allow_bypass(struct regulator *regulator,
+					 bool allow)
+{
+	return 0;
 }
 
 static inline int regulator_register_notifier(struct regulator *regulator,

include/linux/regulator/driver.h

···
 	REGULATOR_STATUS_NORMAL,
 	REGULATOR_STATUS_IDLE,
 	REGULATOR_STATUS_STANDBY,
+	/* The regulator is enabled but not regulating */
+	REGULATOR_STATUS_BYPASS,
 	/* in case that any other status doesn't apply */
 	REGULATOR_STATUS_UNDEFINED,
 };
···
  *	REGULATOR_STATUS value (or negative errno)
  * @get_optimum_mode: Get the most efficient operating mode for the regulator
  *                    when running with the specified parameters.
+ *
+ * @set_bypass: Set the regulator in bypass mode.
+ * @get_bypass: Get the regulator bypass mode state.
  *
  * @enable_time: Time taken for the regulator voltage output voltage to
  *               stabilise after being enabled, in microseconds.
···
 	/* get most efficient regulator operating mode for load */
 	unsigned int (*get_optimum_mode) (struct regulator_dev *, int input_uV,
 					  int output_uV, int load_uA);
+
+	/* control and report on bypass mode */
+	int (*set_bypass)(struct regulator_dev *dev, bool enable);
+	int (*get_bypass)(struct regulator_dev *dev, bool *enable);
 
 	/* the operations below are for configuration of regulator state when
 	 * its parent PMIC enters a global STANDBY/HIBERNATE state */
···
 	int exclusive;
 	u32 use_count;
 	u32 open_count;
+	u32 bypass_count;
 
 	/* lists we belong to */
 	struct list_head list; /* list of all regulators */

include/linux/regulator/machine.h

···
  *           board/machine.
  * STATUS:   Regulator can be enabled and disabled.
  * DRMS:     Dynamic Regulator Mode Switching is enabled for this regulator.
+ * BYPASS:   Regulator can be put into bypass mode
  */
 
 #define REGULATOR_CHANGE_VOLTAGE	0x1
···
 #define REGULATOR_CHANGE_MODE		0x4
 #define REGULATOR_CHANGE_STATUS		0x8
 #define REGULATOR_CHANGE_DRMS		0x10
+#define REGULATOR_CHANGE_BYPASS		0x20
 
 /**
  * struct regulator_state - regulator state during low power system states