[PATCH v2] regulator: core: Resolve supply name earlier to prevent double-init

From: Christian Kohlschütter
Date: Fri Jul 22 2022 - 13:42:38 EST


Previously, an unresolved regulator supply reference upon calling
regulator_register on an always-on or boot-on regulator caused
set_machine_constraints to be called twice.

This in turn may initialize the regulator twice, leading to voltage
glitches that are timing-dependent. A simple, unrelated configuration
change may be enough to hide this problem, only to be surfaced by
chance.

One such example is the SD-Card voltage regulator in a NanoPI R4S that
would not initialize reliably unless the registration flow was just
complex enough to allow the regulator to properly reset between calls.

Fix this by re-arranging regulator_register, trying resolve the
regulator's supply early enough that set_machine_constraints does not
need to be called twice.

Signed-off-by: Christian Kohlschütter <christian@xxxxxxxxxxxxxxxx>
---
drivers/regulator/core.c | 51 +++++++++++++++++++++++++---------------
1 file changed, 32 insertions(+), 19 deletions(-)

diff --git a/drivers/regulator/core.c b/drivers/regulator/core.c
index 398c8d6afd4..5c2b97ea633 100644
--- a/drivers/regulator/core.c
+++ b/drivers/regulator/core.c
@@ -5492,7 +5492,38 @@ regulator_register(const struct regulator_desc *regulator_desc,
BLOCKING_INIT_NOTIFIER_HEAD(&rdev->notifier);
INIT_DELAYED_WORK(&rdev->disable_work, regulator_disable_work);

- /* preform any regulator specific init */
+ /* set regulator constraints */
+ if (init_data)
+ rdev->constraints = kmemdup(&init_data->constraints,
+ sizeof(*rdev->constraints),
+ GFP_KERNEL);
+ else
+ rdev->constraints = kzalloc(sizeof(*rdev->constraints),
+ GFP_KERNEL);
+ if (!rdev->constraints) {
+ ret = -ENOMEM;
+ goto clean;
+ }
+
+ if (init_data && init_data->supply_regulator)
+ rdev->supply_name = init_data->supply_regulator;
+ else if (regulator_desc->supply_name)
+ rdev->supply_name = regulator_desc->supply_name;
+
+ if ((rdev->supply_name && !rdev->supply) && rdev->constraints
+ && (rdev->constraints->always_on || rdev->constraints->boot_on)) {
+ /* Try to resolve the name of the supplying regulator here first
+ * so we prevent double-initializing the regulator, which may
+ * cause timing-specific voltage brownouts/glitches that are
+ * hard to debug.
+ */
+ ret = regulator_resolve_supply(rdev);
+ if (ret)
+ rdev_dbg(rdev, "unable to resolve supply early: %pe\n",
+ ERR_PTR(ret));
+ }
+
+ /* perform any regulator specific init */
if (init_data && init_data->regulator_init) {
ret = init_data->regulator_init(rdev->reg_data);
if (ret < 0)
@@ -5518,24 +5549,6 @@ regulator_register(const struct regulator_desc *regulator_desc,
(unsigned long) atomic_inc_return(&regulator_no));
dev_set_drvdata(&rdev->dev, rdev);

- /* set regulator constraints */
- if (init_data)
- rdev->constraints = kmemdup(&init_data->constraints,
- sizeof(*rdev->constraints),
- GFP_KERNEL);
- else
- rdev->constraints = kzalloc(sizeof(*rdev->constraints),
- GFP_KERNEL);
- if (!rdev->constraints) {
- ret = -ENOMEM;
- goto wash;
- }
-
- if (init_data && init_data->supply_regulator)
- rdev->supply_name = init_data->supply_regulator;
- else if (regulator_desc->supply_name)
- rdev->supply_name = regulator_desc->supply_name;
-
ret = set_machine_constraints(rdev);
if (ret == -EPROBE_DEFER) {
/* Regulator might be in bypass mode and so needs its supply
--
2.36.2