regulator: check that dummy regulator has been probed before using it

Due to asynchronous driver probing there is a chance that the dummy
regulator hasn't already been probed when first accessing it.

Cc: stable@vger.kernel.org
Signed-off-by: Christian Eggers <ceggers@arri.de>
Link: https://patch.msgid.link/20250313103051.32430-3-ceggers@arri.de
Signed-off-by: Mark Brown <broonie@kernel.org>

Author: ceggers-arri

drivers/regulator/core.c

@@ -2074,6 +2074,10 @@ static int regulator_resolve_supply(struct regulator_dev *rdev)
 
 		if (have_full_constraints()) {
 			r = dummy_regulator_rdev;
+			if (!r) {
+				ret = -EPROBE_DEFER;
+				goto out;
+			}
 			get_device(&r->dev);
 		} else {
 			dev_err(dev, "Failed to resolve %s-supply for %s\n",
@@ -2091,6 +2095,10 @@ static int regulator_resolve_supply(struct regulator_dev *rdev)
 			goto out;
 		}
 		r = dummy_regulator_rdev;
+		if (!r) {
+			ret = -EPROBE_DEFER;
+			goto out;
+		}
 		get_device(&r->dev);
 	}
 
@@ -2219,8 +2227,10 @@ struct regulator *_regulator_get_common(struct regulator_dev *rdev, struct devic
 			 * enabled, even if it isn't hooked up, and just
 			 * provide a dummy.
 			 */
-			dev_warn(dev, "supply %s not found, using dummy regulator\n", id);
 			rdev = dummy_regulator_rdev;
+			if (!rdev)
+				return ERR_PTR(-EPROBE_DEFER);
+			dev_warn(dev, "supply %s not found, using dummy regulator\n", id);
 			get_device(&rdev->dev);
 			break;