commit 6492bc1b1a9cb21d28cde3c70d090c7648c8b0ed
author Mark Brown <broonie@opensource.wolfsonmicro.com> Thu Apr 19 13:19:07 2012 +0100
committer Mark Brown <broonie@opensource.wolfsonmicro.com> Fri Apr 20 10:12:38 2012 +0100
tree 864ac01b80bbc6e57cbd86e0938b20112d68fe4a
parent 854ccbaee7e48734936690a3fd4817c57e98aaad

regulator: core: Optimise enable/disable path for always on regulators

If a regulator is always on for any reason then cache that when the
consumer is created and use it to optimise away the need to take locks
or recurse up the supply tree when consumers do enable or disable calls.
The scheduling of asynchronous work for bulk enables is also skipped.

We don't actually check if the device physically supports control on the
basis that constraints allowing status changes on physically always on
regulators are nonsensical anyway.

This is a very common pattern in hardware - it's normal to have some
power supplies that have either no software control or are critical to
system function - so many systems should be able to benefit.

Signed-off-by: Mark Brown <broonie@opensource.wolfsonmicro.com>
Acked-by: Liam Girdwood <lrg@ti.com>

drivers/regulator/core.c

diff --git a/drivers/regulator/core.c b/drivers/regulator/core.c
index 2f0d557..4b2c02c5 100644
--- a/drivers/regulator/core.c
+++ b/drivers/regulator/core.c
@@ -74,6 +74,7 @@
 struct regulator {
 	struct device *dev;
 	struct list_head list;
+	unsigned int always_on:1;
 	int uA_load;
 	int min_uV;
 	int max_uV;
@@ -155,6 +156,17 @@
 	return regnode;
 }
 
+static int _regulator_can_change_status(struct regulator_dev *rdev)
+{
+	if (!rdev->constraints)
+		return 0;
+
+	if (rdev->constraints->valid_ops_mask & REGULATOR_CHANGE_STATUS)
+		return 1;
+	else
+		return 0;
+}
+
 /* Platform voltage constraint check */
 static int regulator_check_voltage(struct regulator_dev *rdev,
 				   int *min_uV, int *max_uV)
@@ -1141,6 +1153,15 @@
 				   &regulator->max_uV);
 	}
 
+	/*
+	 * Check now if the regulator is an always on regulator - if
+	 * it is then we don't need to do nearly so much work for
+	 * enable/disable calls.
+	 */
+	if (!_regulator_can_change_status(rdev) &&
+	    _regulator_is_enabled(rdev))
+		regulator->always_on = true;
+
 	mutex_unlock(&rdev->mutex);
 	return regulator;
 link_name_err:
@@ -1443,17 +1464,6 @@
 }
 EXPORT_SYMBOL_GPL(devm_regulator_put);
 
-static int _regulator_can_change_status(struct regulator_dev *rdev)
-{
-	if (!rdev->constraints)
-		return 0;
-
-	if (rdev->constraints->valid_ops_mask & REGULATOR_CHANGE_STATUS)
-		return 1;
-	else
-		return 0;
-}
-
 /* locks held by regulator_enable() */
 static int _regulator_enable(struct regulator_dev *rdev)
 {
@@ -1533,6 +1543,9 @@
 	struct regulator_dev *rdev = regulator->rdev;
 	int ret = 0;
 
+	if (regulator->always_on)
+		return 0;
+
 	if (rdev->supply) {
 		ret = regulator_enable(rdev->supply);
 		if (ret != 0)
@@ -1611,6 +1624,9 @@
 	struct regulator_dev *rdev = regulator->rdev;
 	int ret = 0;
 
+	if (regulator->always_on)
+		return 0;
+
 	mutex_lock(&rdev->mutex);
 	ret = _regulator_disable(rdev);
 	mutex_unlock(&rdev->mutex);
@@ -1719,6 +1735,9 @@
 	struct regulator_dev *rdev = regulator->rdev;
 	int ret;
 
+	if (regulator->always_on)
+		return 0;
+
 	mutex_lock(&rdev->mutex);
 	rdev->deferred_disables++;
 	mutex_unlock(&rdev->mutex);
@@ -1757,6 +1776,9 @@
 {
 	int ret;
 
+	if (regulator->always_on)
+		return 1;
+
 	mutex_lock(&regulator->rdev->mutex);
 	ret = _regulator_is_enabled(regulator->rdev);
 	mutex_unlock(&regulator->rdev->mutex);
@@ -2539,9 +2561,13 @@
 	int i;
 	int ret = 0;
 
-	for (i = 0; i < num_consumers; i++)
-		async_schedule_domain(regulator_bulk_enable_async,
-				      &consumers[i], &async_domain);
+	for (i = 0; i < num_consumers; i++) {
+		if (consumers[i].consumer->always_on)
+			consumers[i].ret = 0;
+		else
+			async_schedule_domain(regulator_bulk_enable_async,
+					      &consumers[i], &async_domain);
+	}
 
 	async_synchronize_full_domain(&async_domain);