regulator: core: Resolve supply name earlier to prevent double-init

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>
Link: https://lore.kernel.org/r/20220818124646.6005-1-christian@kohlschutter.com
Signed-off-by: Mark Brown <broonie@kernel.org>

diff --git a/drivers/regulator/core.c b/drivers/regulator/core.c
index d8373cb..a5033c6 100644 (file)
--- a/drivers/regulator/core.c
+++ b/drivers/regulator/core.c
@@ -5496,7 +5496,39 @@ 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->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)
@@ -5522,24 +5554,6 @@ 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