regulator: Add option for machine drivers to enable the dummy regulator

Allow machine drivers to explicitly enable the use of the dummy regulator,
enabling simpler support for systems with only a few specific supplies
visible to software.

It is strongly recommended that this is not used on systems with
substantial software control over their PMICs, for maximum functionality
constrints should be as fully specified as possible.

Signed-off-by: Mark Brown <[e-mail]>
Signed-off-by: Liam Girdwood <[e-mail]>

drivers/regulator/Makefile

···
 #
 
 
-obj-$(CONFIG_REGULATOR) += core.o
+obj-$(CONFIG_REGULATOR) += core.o dummy.o
 obj-$(CONFIG_REGULATOR_FIXED_VOLTAGE) += fixed.o
 obj-$(CONFIG_REGULATOR_VIRTUAL_CONSUMER) += virtual.o
 obj-$(CONFIG_REGULATOR_USERSPACE_CONSUMER) += userspace-consumer.o
 
 obj-$(CONFIG_REGULATOR_AD5398) += ad5398.o
 obj-$(CONFIG_REGULATOR_BQ24022) += bq24022.o
-obj-$(CONFIG_REGULATOR_DUMMY) += dummy.o
 obj-$(CONFIG_REGULATOR_LP3971) += lp3971.o
 obj-$(CONFIG_REGULATOR_LP3972) += lp3972.o
 obj-$(CONFIG_REGULATOR_MAX1586) += max1586.o

drivers/regulator/core.c

···
 static LIST_HEAD(regulator_list);
 static LIST_HEAD(regulator_map_list);
 static int has_full_constraints;
+static bool board_wants_dummy_regulator;
 
 /*
  * struct regulator_map
···
 			rdev = map->regulator;
 			goto found;
 		}
+	}
+
+	if (board_wants_dummy_regulator) {
+		rdev = dummy_regulator_rdev;
+		goto found;
 	}
 
 #ifdef CONFIG_REGULATOR_DUMMY
···
 	has_full_constraints = 1;
 }
 EXPORT_SYMBOL_GPL(regulator_has_full_constraints);
+
+/**
+ * regulator_use_dummy_regulator - Provide a dummy regulator when none is found
+ *
+ * Calling this function will cause the regulator API to provide a
+ * dummy regulator to consumers if no physical regulator is found,
+ * allowing most consumers to proceed as though a regulator were
+ * configured.  This allows systems such as those with software
+ * controllable regulators for the CPU core only to be brought up more
+ * readily.
+ */
+void regulator_use_dummy_regulator(void)
+{
+	board_wants_dummy_regulator = true;
+}
+EXPORT_SYMBOL_GPL(regulator_use_dummy_regulator);
 
 /**
  * rdev_get_drvdata - get rdev regulator driver data

include/linux/regulator/machine.h

···
 
 #ifdef CONFIG_REGULATOR
 void regulator_has_full_constraints(void);
+void regulator_use_dummy_regulator(void);
 #else
 static inline void regulator_has_full_constraints(void)
+{
+}
+
+static inline void regulator_use_dummy_regulator(void)
 {
 }
 #endif