linux-kernel - [PATCH v3] regulator: core: Resolve supply name earlier to prevent double-init

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Date:   Thu, 4 Aug 2022 12:44:29 +0200
From:   Christian Kohlschütter 
        <christian@...lschutter.com>
To:     Vincent Legoll <vincent.legoll@...il.com>,
        Mark Brown <broonie@...nel.org>
Cc:     Heiko Stübner <heiko@...ech.de>,
        Liam Girdwood <lgirdwood@...il.com>,
        linux-arm-kernel <linux-arm-kernel@...ts.infradead.org>,
        linux-kernel <linux-kernel@...r.kernel.org>,
        Linux MMC List <linux-mmc@...r.kernel.org>,
        "open list:ARM/Rockchip SoC..." <linux-rockchip@...ts.infradead.org>,
        Markus Reichl <m.reichl@...etechno.de>,
        Robin Murphy <robin.murphy@....com>, wens@...nel.org
Subject: [PATCH v3] 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 Kohlsch=C3=BCtter <christian@...lschutter.com>
---
 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);
=20
-	/* preform any regulator specific init */
+	/* set regulator constraints */
+	if (init_data)
+		rdev->constraints =3D kmemdup(&init_data->constraints,
+					    sizeof(*rdev->constraints),
+					    GFP_KERNEL);
+	else
+		rdev->constraints =3D =
kzalloc(sizeof(*rdev->constraints),
+					    GFP_KERNEL);
+	if (!rdev->constraints) {
+		ret =3D -ENOMEM;
+		goto clean;
+	}
+
+	if (init_data && init_data->supply_regulator)
+		rdev->supply_name =3D init_data->supply_regulator;
+	else if (regulator_desc->supply_name)
+		rdev->supply_name =3D 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 =3D 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 =3D 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);
=20
-	/* set regulator constraints */
-	if (init_data)
-		rdev->constraints =3D kmemdup(&init_data->constraints,
-					    sizeof(*rdev->constraints),
-					    GFP_KERNEL);
-	else
-		rdev->constraints =3D =
kzalloc(sizeof(*rdev->constraints),
-					    GFP_KERNEL);
-	if (!rdev->constraints) {
-		ret =3D -ENOMEM;
-		goto wash;
-	}
-
-	if (init_data && init_data->supply_regulator)
-		rdev->supply_name =3D init_data->supply_regulator;
-	else if (regulator_desc->supply_name)
-		rdev->supply_name =3D regulator_desc->supply_name;
-
 	ret =3D set_machine_constraints(rdev);
 	if (ret =3D=3D -EPROBE_DEFER) {
 		/* Regulator might be in bypass mode and so needs its =
supply
--=20
2.36.2