[PATCH v5] regulator: core: Resolve supply name earlier to prevent double-init

["Christian Kohlschütter" <christian@kohlschutter.com>]

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@kohlschutter.com>
---
 drivers/regulator/core.c | 58 ++++++++++++++++++++++++----------------
 1 file changed, 35 insertions(+), 23 deletions(-)

diff --git a/drivers/regulator/core.c b/drivers/regulator/core.c
index 77f60eef960..2ff0ab2730f 100644
--- a/drivers/regulator/core.c
+++ b/drivers/regulator/core.c
@@ -5391,6 +5391,7 @@ regulator_register(const struct regulator_desc *regulator_desc,
 	bool dangling_of_gpiod = false;
 	struct device *dev;
 	int ret, i;
+	bool resolved_early = false;
 
 	if (cfg == NULL)
 		return ERR_PTR(-EINVAL);
@@ -5494,24 +5495,10 @@ 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 */
-	if (init_data && init_data->regulator_init) {
-		ret = init_data->regulator_init(rdev->reg_data);
-		if (ret < 0)
-			goto clean;
-	}
-
-	if (config->ena_gpiod) {
-		ret = regulator_ena_gpio_request(rdev, config);
-		if (ret != 0) {
-			rdev_err(rdev, "Failed to request enable GPIO: %pe\n",
-				 ERR_PTR(ret));
-			goto clean;
-		}
-		/* The regulator core took over the GPIO descriptor */
-		dangling_cfg_gpiod = false;
-		dangling_of_gpiod = false;
-	}
+	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;
 
 	/* register with sysfs */
 	rdev->dev.class = &regulator_class;
@@ -5533,13 +5520,38 @@ regulator_register(const struct regulator_desc *regulator_desc,
 		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;
+	if ((rdev->supply_name && !rdev->supply) &&
+		(rdev->constraints->always_on ||
+		 rdev->constraints->boot_on)) {
+		ret = regulator_resolve_supply(rdev);
+		if (ret != 0)
+			rdev_dbg(rdev, "Unable to resolve supply early: %pe\n",
+				 ERR_PTR(ret));
+
+		resolved_early = true;
+	}
+
+	/* perform any regulator specific init */
+	if (init_data && init_data->regulator_init) {
+		ret = init_data->regulator_init(rdev->reg_data);
+		if (ret < 0)
+			goto wash;
+	}
+
+	if (config->ena_gpiod) {
+		ret = regulator_ena_gpio_request(rdev, config);
+		if (ret != 0) {
+			rdev_err(rdev, "Failed to request enable GPIO: %pe\n",
+					 ERR_PTR(ret));
+			goto wash;
+		}
+		/* The regulator core took over the GPIO descriptor */
+		dangling_cfg_gpiod = false;
+		dangling_of_gpiod = false;
+	}
 
 	ret = set_machine_constraints(rdev);
-	if (ret == -EPROBE_DEFER) {
+	if (ret == -EPROBE_DEFER && !resolved_early) {
 		/* Regulator might be in bypass mode and so needs its supply
 		 * to set the constraints
 		 */
-- 
2.36.2