dt-bindings: power: supply: maxim,max8903: add DC and USB input current-limit controls

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@herrie.org>
Reviewed-by: Rob Herring (Arm) <robh@kernel.org>
Link: https://patch.msgid.link/20260605-submit-power-max8903-dc-limit-v2-1-0c5396e98f14@herrie.org
Signed-off-by: Sebastian Reichel <sebastian.reichel@collabora.com>

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>;
+    };