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, 9 insertions, 0 deletions

diff --git a/include/linux/regulator/driver.h b/include/linux/regulator/driver.h
index 0cf37bc..2255468 100644
--- a/include/linux/regulator/driver.h
+++ b/include/linux/regulator/driver.h
@@ -45,6 +45,10 @@ enum regulator_status {
  * @set_voltage: Set the voltage for the regulator within the range specified.
  *               The driver should select the voltage closest to min_uV.
  * @get_voltage: Return the currently configured voltage for the regulator.
+ * @list_voltage: Return one of the supported voltages, in microvolts; zero
+ *	if the selector indicates a voltage that is unusable on this system;
+ *	or negative errno.  Selectors range from zero to one less than
+ *	regulator_desc.n_voltages.  Voltages may be reported in any order.
  *
  * @set_current_limit: Configure a limit for a current-limited regulator.
  * @get_current_limit: Get the limit for a current-limited regulator.
@@ -66,6 +70,9 @@ enum regulator_status {
  */
 struct regulator_ops {
 
+	/* enumerate supported voltages */
+	int (*list_voltage) (struct regulator_dev *, unsigned selector);
+
 	/* get/set regulator voltage */
 	int (*set_voltage) (struct regulator_dev *, int min_uV, int max_uV);
 	int (*get_voltage) (struct regulator_dev *);
@@ -124,6 +131,7 @@ enum regulator_type {
  *
  * @name: Identifying name for the regulator.
  * @id: Numerical identifier for the regulator.
+ * @n_voltages: Number of selectors available for ops.list_voltage().
  * @ops: Regulator operations table.
  * @irq: Interrupt number for the regulator.
  * @type: Indicates if the regulator is a voltage or current regulator.
@@ -132,6 +140,7 @@ enum regulator_type {
 struct regulator_desc {
 	const char *name;
 	int id;
+	unsigned n_voltages;
 	struct regulator_ops *ops;
 	int irq;
 	enum regulator_type type;