regulator: core: move supply check earlier in set_machine_constraints()

Since commit 98e48cd ("regulator: core: resolve supply for
boot-on/always-on regulators"), set_machine_constraints() can return
-EPROBE_DEFER very late, after it has done a lot of work and
configuration of the regulator.

This means that configuration will happen multiple times for no
benefit in that case. Furthermore, this can lead to timing-dependent
voltage glitches as mentioned e.g. in commit 8a866d5 ("regulator:
core: Resolve supply name earlier to prevent double-init").

We can know that it's going to fail very early, in particular before
going through the complete regulator configuration by moving some code
around a little.

Do so to avoid re-configuring the regulator multiple times, also
avoiding the voltage glitches if we can.

Fixes: 98e48cd ("regulator: core: resolve supply for boot-on/always-on regulators")
Signed-off-by: André Draszik <andre.draszik@linaro.org>
Link: https://patch.msgid.link/20260109-regulators-defer-v2-3-1a25dc968e60@linaro.org
Signed-off-by: Mark Brown <broonie@kernel.org>

Author: andred

drivers/regulator/core.c

@@ -1444,6 +1444,33 @@ static int set_machine_constraints(struct regulator_dev *rdev)
 	int ret = 0;
 	const struct regulator_ops *ops = rdev->desc->ops;
 
+	/*
+	 * If there is no mechanism for controlling the regulator then
+	 * flag it as always_on so we don't end up duplicating checks
+	 * for this so much.  Note that we could control the state of
+	 * a supply to control the output on a regulator that has no
+	 * direct control.
+	 */
+	if (!rdev->ena_pin && !ops->enable) {
+		if (rdev->supply_name && !rdev->supply)
+			return -EPROBE_DEFER;
+
+		if (rdev->supply)
+			rdev->constraints->always_on =
+				rdev->supply->rdev->constraints->always_on;
+		else
+			rdev->constraints->always_on = true;
+	}
+
+	/*
+	 * If we want to enable this regulator, make sure that we know the
+	 * supplying regulator.
+	 */
+	if (rdev->constraints->always_on || rdev->constraints->boot_on) {
+		if (rdev->supply_name && !rdev->supply)
+			return -EPROBE_DEFER;
+	}
+
 	ret = machine_constraints_voltage(rdev, rdev->constraints);
 	if (ret != 0)
 		return ret;
@@ -1609,37 +1636,15 @@ static int set_machine_constraints(struct regulator_dev *rdev)
 		}
 	}
 
-	/*
-	 * If there is no mechanism for controlling the regulator then
-	 * flag it as always_on so we don't end up duplicating checks
-	 * for this so much.  Note that we could control the state of
-	 * a supply to control the output on a regulator that has no
-	 * direct control.
-	 */
-	if (!rdev->ena_pin && !ops->enable) {
-		if (rdev->supply_name && !rdev->supply)
-			return -EPROBE_DEFER;
-
-		if (rdev->supply)
-			rdev->constraints->always_on =
-				rdev->supply->rdev->constraints->always_on;
-		else
-			rdev->constraints->always_on = true;
-	}
-
 	/* If the constraints say the regulator should be on at this point
 	 * and we have control then make sure it is enabled.
 	 */
 	if (rdev->constraints->always_on || rdev->constraints->boot_on) {
 		bool supply_enabled = false;
 
-		/* If we want to enable this regulator, make sure that we know
-		 * the supplying regulator.
-		 */
-		if (rdev->supply_name && !rdev->supply)
-			return -EPROBE_DEFER;
-
-		/* If supplying regulator has already been enabled,
+		/* We have ensured a potential supply has been resolved above.
+		 *
+		 * If supplying regulator has already been enabled,
 		 * it's not intended to have use_count increment
 		 * when rdev is only boot-on.
 		 */