[PATCH v2 1/2] dt-bindings: power: supply: maxim,max8903: add DC and USB input current-limit controls
From: Herman van Hazendonk via B4 Relay
Date: Fri Jun 05 2026 - 05:36:24 EST
From: Herman van Hazendonk <github.com@xxxxxxxxxx>
Add three optional properties to the MAX8903 charger binding to
describe board-level GPIO control of the DC and USB input current
limits:
DC input (TA / DOK pin):
- dc-current-limit-gpios (1..4 GPIOs): mux control lines feeding
the MAX8903 IDC resistor mux;
- dc-current-limit-mapping (uint32-matrix of {microamps,
gpio_bit_pattern} pairs): the available current levels and the
GPIO bit pattern that selects each level.
USB input (USB / UOK pin):
- usb-current-limit-gpios: a single GPIO driving the IUSB pin.
The IUSB pin is silicon-fixed by the MAX8903 datasheet (Pin
Description): low selects 100 mA, high selects 500 mA. Only
the GPIO mapping is board-specific; the current values are
not exposed in DT.
A dependentRequired block ties dc-current-limit-gpios and
dc-current-limit-mapping together so an incomplete DT cannot pass
validation with only one half of the pair.
These let userspace clamp the input draw via the standard
POWER_SUPPLY_PROP_INPUT_CURRENT_LIMIT power_supply attribute. The HP
TouchPad uses both: two TLMM lines select between 0.5 A, 1.0 A,
1.5 A and 2.0 A DC input current limits behind the MAX8903B
charger, and a third TLMM line picks the IUSB 100 mA / 500 mA
limit.
These are purely additive; existing platforms remain unaffected.
Signed-off-by: Herman van Hazendonk <github.com@xxxxxxxxxx>
---
.../bindings/power/supply/maxim,max8903.yaml | 53 ++++++++++++++++++++++
1 file changed, 53 insertions(+)
diff --git a/Documentation/devicetree/bindings/power/supply/maxim,max8903.yaml b/Documentation/devicetree/bindings/power/supply/maxim,max8903.yaml
index 86af38378999..b3d8c0a5f214 100644
--- a/Documentation/devicetree/bindings/power/supply/maxim,max8903.yaml
+++ b/Documentation/devicetree/bindings/power/supply/maxim,max8903.yaml
@@ -44,9 +44,40 @@ properties:
maxItems: 1
description: USB suspend pin (active high, output)
+ dc-current-limit-gpios:
+ minItems: 1
+ maxItems: 4
+ description:
+ GPIOs controlling DC input current limit via resistor mux.
+ Used with dc-current-limit-mapping to select charging current.
+
+ dc-current-limit-mapping:
+ $ref: /schemas/types.yaml#/definitions/uint32-matrix
+ minItems: 2
+ maxItems: 16
+ description: |
+ Array of (current_microamps, gpio_bit_pattern) pairs defining available
+ DC current limits. The gpio_bit_pattern is applied to dc-current-limit-gpios
+ to select that current level.
+ items:
+ items:
+ - description: Current limit in microamps
+ - description: GPIO bit pattern value
+
+ usb-current-limit-gpios:
+ maxItems: 1
+ description:
+ GPIO driving the MAX8903 IUSB pin. IUSB is a silicon-fixed
+ two-state input - low selects 100 mA, high selects 500 mA.
+ Only the GPIO mapping is board-specific.
+
required:
- compatible
+dependentRequired:
+ dc-current-limit-gpios: [dc-current-limit-mapping]
+ dc-current-limit-mapping: [dc-current-limit-gpios]
+
anyOf:
- required:
- dok-gpios
@@ -65,3 +96,25 @@ examples:
chg-gpios = <&gpio3 15 GPIO_ACTIVE_LOW>;
cen-gpios = <&gpio2 5 GPIO_ACTIVE_LOW>;
};
+ - |
+ /* Example with DC and USB current limit control */
+ #include <dt-bindings/gpio/gpio.h>
+ charger {
+ compatible = "maxim,max8903";
+ dok-gpios = <&gpio2 3 GPIO_ACTIVE_LOW>;
+ flt-gpios = <&gpio2 2 GPIO_ACTIVE_LOW>;
+ chg-gpios = <&gpio3 15 GPIO_ACTIVE_LOW>;
+ cen-gpios = <&gpio2 5 GPIO_ACTIVE_LOW>;
+ dcm-gpios = <&gpio2 6 GPIO_ACTIVE_HIGH>;
+
+ /* DC input current limit via IDC resistor mux */
+ dc-current-limit-gpios = <&gpio1 0 GPIO_ACTIVE_HIGH>,
+ <&gpio1 1 GPIO_ACTIVE_HIGH>;
+ dc-current-limit-mapping = <750000 0>, /* GPIO[1:0]=0b00 */
+ <900000 1>, /* GPIO[1:0]=0b01 */
+ <1400000 3>, /* GPIO[1:0]=0b11 */
+ <2000000 2>; /* GPIO[1:0]=0b10 */
+
+ /* USB current limit: IUSB pin, 100 mA (low) / 500 mA (high) */
+ usb-current-limit-gpios = <&gpio1 2 GPIO_ACTIVE_HIGH>;
+ };
--
2.43.0