regulator: enumerate voltages (v2)

Add a basic mechanism for regulators to report the discrete
voltages they support:  list_voltage() enumerates them using
selectors numbered from 0 to an upper bound.

Use those methods to force machine-level constraints into bounds.
(Example:  regulator supports 1.8V, 2.4V, 2.6V, 3.3V, and board
constraints for that rail are 2.0V to 3.6V ... so the range of
voltages is then 2.4V to 3.3V on this board.)

Export those voltages to the regulator consumer interface, so for
example regulator hooked up to an MMC/SD/SDIO slot can report the
actual voltage options available to cards connected there.

Signed-off-by: David Brownell <dbrownell@users.sourceforge.net>
Acked-by: Mark Brown <broonie@opensource.wolfsonmicro.com>
Signed-off-by: Liam Girdwood <lrg@slimlogic.co.uk>

1 files changed, 113 insertions, 0 deletions

diff --git a/drivers/regulator/core.c b/drivers/regulator/core.c
index 75abcd8..da357a0 100644
--- a/drivers/regulator/core.c
+++ b/drivers/regulator/core.c
@@ -692,6 +692,69 @@ static int set_machine_constraints(struct regulator_dev *rdev,
 	else
 		name = "regulator";
 
+	/* constrain machine-level voltage specs to fit
+	 * the actual range supported by this regulator.
+	 */
+	if (ops->list_voltage && rdev->desc->n_voltages) {
+		int	count = rdev->desc->n_voltages;
+		int	i;
+		int	min_uV = INT_MAX;
+		int	max_uV = INT_MIN;
+		int	cmin = constraints->min_uV;
+		int	cmax = constraints->max_uV;
+
+		/* it's safe to autoconfigure fixed-voltage supplies */
+		if (count == 1 && !cmin) {
+			cmin = INT_MIN;
+			cmax = INT_MAX;
+		}
+
+		/* else require explicit machine-level constraints */
+		else if (cmin <= 0 || cmax <= 0 || cmax < cmin) {
+			pr_err("%s: %s '%s' voltage constraints\n",
+				       __func__, "invalid", name);
+			ret = -EINVAL;
+			goto out;
+		}
+
+		/* initial: [cmin..cmax] valid, [min_uV..max_uV] not */
+		for (i = 0; i < count; i++) {
+			int	value;
+
+			value = ops->list_voltage(rdev, i);
+			if (value <= 0)
+				continue;
+
+			/* maybe adjust [min_uV..max_uV] */
+			if (value >= cmin && value < min_uV)
+				min_uV = value;
+			if (value <= cmax && value > max_uV)
+				max_uV = value;
+		}
+
+		/* final: [min_uV..max_uV] valid iff constraints valid */
+		if (max_uV < min_uV) {
+			pr_err("%s: %s '%s' voltage constraints\n",
+				       __func__, "unsupportable", name);
+			ret = -EINVAL;
+			goto out;
+		}
+
+		/* use regulator's subset of machine constraints */
+		if (constraints->min_uV < min_uV) {
+			pr_debug("%s: override '%s' %s, %d -> %d\n",
+				       __func__, name, "min_uV",
+					constraints->min_uV, min_uV);
+			constraints->min_uV = min_uV;
+		}
+		if (constraints->max_uV > max_uV) {
+			pr_debug("%s: override '%s' %s, %d -> %d\n",
+				       __func__, name, "max_uV",
+					constraints->max_uV, max_uV);
+			constraints->max_uV = max_uV;
+		}
+	}
+
 	rdev->constraints = constraints;
 
 	/* do we need to apply the constraint voltage */
@@ -1251,6 +1314,56 @@ int regulator_is_enabled(struct regulator *regulator)
 EXPORT_SYMBOL_GPL(regulator_is_enabled);
 
 /**
+ * regulator_count_voltages - count regulator_list_voltage() selectors
+ * @regulator: regulator source
+ *
+ * Returns number of selectors, or negative errno.  Selectors are
+ * numbered starting at zero, and typically correspond to bitfields
+ * in hardware registers.
+ */
+int regulator_count_voltages(struct regulator *regulator)
+{
+	struct regulator_dev	*rdev = regulator->rdev;
+
+	return rdev->desc->n_voltages ? : -EINVAL;
+}
+EXPORT_SYMBOL_GPL(regulator_count_voltages);
+
+/**
+ * regulator_list_voltage - enumerate supported voltages
+ * @regulator: regulator source
+ * @selector: identify voltage to list
+ * Context: can sleep
+ *
+ * Returns a voltage that can be passed to @regulator_set_voltage(),
+ * zero if this selector code can't be used on this sytem, or a
+ * negative errno.
+ */
+int regulator_list_voltage(struct regulator *regulator, unsigned selector)
+{
+	struct regulator_dev	*rdev = regulator->rdev;
+	struct regulator_ops	*ops = rdev->desc->ops;
+	int			ret;
+
+	if (!ops->list_voltage || selector >= rdev->desc->n_voltages)
+		return -EINVAL;
+
+	mutex_lock(&rdev->mutex);
+	ret = ops->list_voltage(rdev, selector);
+	mutex_unlock(&rdev->mutex);
+
+	if (ret > 0) {
+		if (ret < rdev->constraints->min_uV)
+			ret = 0;
+		else if (ret > rdev->constraints->max_uV)
+			ret = 0;
+	}
+
+	return ret;
+}
+EXPORT_SYMBOL_GPL(regulator_list_voltage);
+
+/**
  * regulator_set_voltage - set regulator output voltage
  * @regulator: regulator source
  * @min_uV: Minimum required voltage in uV