Re: [PATCH 1/2] dt-bindings: power: supply: maxim,max8903: add DC and USB input current-limit controls

[Sebastian Reichel <sebastian.reichel@collabora.com>]

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Hi,

On Wed, Jun 03, 2026 at 09:15:18AM +0200, Herman van Hazendonk wrote:
> Add four 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
>     tri-state pin (low / high);
>   - usb-current-limit-values: the two microamp values that the IUSB
>     pin selects.
>
> 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@herrie.org>
> ---
>  .../bindings/power/supply/maxim,max8903.yaml  | 58 +++++++++++++++++++
>  1 file changed, 58 insertions(+)
> 
> diff --git a/Documentation/devicetree/bindings/power/supply/maxim,max8903.yaml b/Documentation/devicetree/bindings/power/supply/maxim,max8903.yaml
> index 86af38378999..5e970ebc08df 100644
> --- a/Documentation/devicetree/bindings/power/supply/maxim,max8903.yaml
> +++ b/Documentation/devicetree/bindings/power/supply/maxim,max8903.yaml
> @@ -44,6 +44,41 @@ 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 controlling USB input current limit.
> +      Low = usb-current-limit-values[0], High = usb-current-limit-values[1].
> +
> +  usb-current-limit-values:
> +    $ref: /schemas/types.yaml#/definitions/uint32-array
> +    minItems: 2
> +    maxItems: 2
> +    default: [100000, 500000]
> +    description:
> +      USB current limits in microamps for GPIO low and high states.
> +      Default is 100mA (low) and 500mA (high) per USB specification.

The IUSB pin always selects between 100mA and 500mA for the MAX8903
according to the datasheet, so why is there a DT property?

Greetings,

-- Sebastian

> +
>  required:
>    - compatible
>  
> @@ -65,3 +100,26 @@ 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-with-current-limit {
> +      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 control */
> +      usb-current-limit-gpios = <&gpio1 2 GPIO_ACTIVE_HIGH>;
> +      usb-current-limit-values = <100000 500000>; /* 100mA / 500mA */
> +    };
> -- 
> 2.43.0
> 

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