[PATCH 2/6] regulator: core: introduce function to lock regulators and its supplies

From: Sascha Hauer
Date: Wed Sep 30 2015 - 09:58:41 EST


Each regulator_dev is locked with its own mutex. This is fine as long
as only one regulator_dev is locked, but makes lockdep unhappy when we
have to walk up the supply chain like it can happen in
regulator_get_voltage:

regulator_get_voltage ->
mutex_lock(&regulator->rdev->mutex) ->
_regulator_get_voltage(regulator->rdev) ->
regulator_get_voltage(rdev->supply) ->
mutex_lock(&regulator->rdev->mutex);

This causes lockdep to issue a possible deadlock warning.

There are at least two ways to work around this:

- We can always lock the whole supply chain using the functions
introduced with this patch.
- We could store the current voltage in struct regulator_rdev so
that we do not have to walk up the supply chain for the
_regulator_get_voltage case.

Anyway, regulator_lock_supply/regulator_unlock_supply will be needed
once we allow regulator_set_voltage to optimize the supply voltages.

Signed-off-by: Sascha Hauer <s.hauer@xxxxxxxxxxxxxx>
---
drivers/regulator/core.c | 39 +++++++++++++++++++++++++++++++++++++++
1 file changed, 39 insertions(+)

diff --git a/drivers/regulator/core.c b/drivers/regulator/core.c
index bd9db70..e5de3d9 100644
--- a/drivers/regulator/core.c
+++ b/drivers/regulator/core.c
@@ -132,6 +132,45 @@ static bool have_full_constraints(void)
}

/**
+ * regulator_lock_supply - lock a regulator and its supplies
+ * @rdev: regulator source
+ */
+static void regulator_lock_supply(struct regulator_dev *rdev)
+{
+ struct regulator *supply;
+ int i = 0;
+
+ while (1) {
+ mutex_lock_nested(&rdev->mutex, i++);
+ supply = rdev->supply;
+
+ if (!rdev->supply)
+ return;
+
+ rdev = supply->rdev;
+ }
+}
+
+/**
+ * regulator_unlock_supply - unlock a regulator and its supplies
+ * @rdev: regulator source
+ */
+static void regulator_unlock_supply(struct regulator_dev *rdev)
+{
+ struct regulator *supply;
+
+ while (1) {
+ mutex_unlock(&rdev->mutex);
+ supply = rdev->supply;
+
+ if (!rdev->supply)
+ return;
+
+ rdev = supply->rdev;
+ }
+}
+
+/**
* of_get_regulator - get a regulator device node based on supply name
* @dev: Device pointer for the consumer (of regulator) device
* @supply: regulator supply name
--
2.5.3

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