linux-kernel - [PATCH RFC] regulator: core: fix constraints handling if current state out of range

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Message-Id: <20251103-regu-fix-v1-1-c8a46581c850@kernel.org>
Date: Mon, 03 Nov 2025 20:32:41 +0100
From: Andreas Kemnade <akemnade@...nel.org>
To: Liam Girdwood <lgirdwood@...il.com>, Mark Brown <broonie@...nel.org>
Cc: linux-kernel@...r.kernel.org, Andreas Kemnade <akemnade@...nel.org>
Subject: [PATCH RFC] regulator: core: fix constraints handling if current
 state out of range

Given a regulator set to an initially out of constraints value,
which cannot be set to the exact voltage given in the min or max constraints,
current code tries to apply a fixed value which obviously fails.

To fix that, allow a range as a constraint in out of bound cases.

A practical use case for this scenario is if there is a quotient
in uV_step which needs to get rounded.
The devicetree should describe the hardware and not depend on the
idea of a specific driver implementation how to round things,
so a small range need to be specified.
Instead of rounding uV_step another user of the devicetree
might be specifying uV_max and uV_min and therefore only needs
to round the end result leading to slightly different results.

Stumbled upon it while creating a regulator with uV_step = 5000000 / 255

Signed-off-by: Andreas Kemnade <akemnade@...nel.org>
Fixes: fa93fd4ecc9c ("regulator: core: Ensure we are at least in bounds for our constraints")
---
not tested yet to avoid magic smoke in case of errors. I rather prefer
having a second pair of eyes on it in this sensitive area.
---
 drivers/regulator/core.c | 8 ++------
 1 file changed, 2 insertions(+), 6 deletions(-)

diff --git a/drivers/regulator/core.c b/drivers/regulator/core.c
index dd7b10e768c0..6b491c21ec5b 100644
--- a/drivers/regulator/core.c
+++ b/drivers/regulator/core.c
@@ -1238,13 +1238,9 @@ static int machine_constraints_voltage(struct regulator_dev *rdev,
 		target_min = current_uV;
 		target_max = current_uV;
 
-		if (current_uV < rdev->constraints->min_uV) {
+		if ((current_uV < rdev->constraints->min_uV) ||
+		    (current_uV > rdev->constraints->max_uV)) {
 			target_min = rdev->constraints->min_uV;
-			target_max = rdev->constraints->min_uV;
-		}
-
-		if (current_uV > rdev->constraints->max_uV) {
-			target_min = rdev->constraints->max_uV;
 			target_max = rdev->constraints->max_uV;
 		}
 

---
base-commit: dcb6fa37fd7bc9c3d2b066329b0d27dedf8becaa
change-id: 20251103-regu-fix-d650274afa89

Best regards,
--  
Andreas Kemnade <akemnade@...nel.org>