dt-bindings: leds: Add DT binding for Richtek RT8515

Add a YAML devicetree binding for the Richtek RT8515
dual channel flash/torch LED driver.

Cc: Sakari Ailus <sakari.ailus@iki.fi>
Cc: newbytee@protonmail.com
Cc: Stephan Gerhold <stephan@gerhold.net>
Cc: phone-devel@vger.kernel.org
Cc: linux-media@vger.kernel.org
Cc: devicetree@vger.kernel.org
Reviewed-by: Rob Herring <robh@kernel.org>
Reviewed-by: Sakari Ailus <sakari.ailus@linux.intel.com>
Signed-off-by: Linus Walleij <linus.walleij@linaro.org>
Signed-off-by: Pavel Machek <pavel@ucw.cz>

Documentation/devicetree/bindings/leds/richtek,rt8515.yaml

+# SPDX-License-Identifier: (GPL-2.0-only OR BSD-2-Clause)
+%YAML 1.2
+---
+$id: http://devicetree.org/schemas/leds/richtek,rt8515.yaml#
+$schema: http://devicetree.org/meta-schemas/core.yaml#
+
+title: Richtek RT8515 1.5A dual channel LED driver
+
+maintainers:
+  - Linus Walleij <linus.walleij@linaro.org>
+
+description: |
+  The Richtek RT8515 is a dual channel (two mode) LED driver that
+  supports driving a white LED in flash or torch mode. The maximum
+  current for each mode is defined in hardware using two resistors
+  RFS and RTS.
+
+properties:
+  compatible:
+    const: richtek,rt8515
+
+  enf-gpios:
+    maxItems: 1
+    description: A connection to the 'ENF' (enable flash) pin.
+
+  ent-gpios:
+    maxItems: 1
+    description: A connection to the 'ENT' (enable torch) pin.
+
+  richtek,rfs-ohms:
+    minimum: 7680
+    maximum: 367000
+    description: The resistance value of the RFS resistor. This
+      resistors limits the maximum flash current. This must be set
+      for the property flash-max-microamp to work, the RFS resistor
+      defines the range of the dimmer setting (brightness) of the
+      flash LED.
+
+  richtek,rts-ohms:
+    minimum: 7680
+    maximum: 367000
+    description: The resistance value of the RTS resistor. This
+      resistors limits the maximum torch current. This must be set
+      for the property torch-max-microamp to work, the RTS resistor
+      defines the range of the dimmer setting (brightness) of the
+      torch LED.
+
+  led:
+    type: object
+    $ref: common.yaml#
+    properties:
+      function: true
+      color: true
+      flash-max-timeout-us: true
+
+      flash-max-microamp:
+        maximum: 700000
+        description: The maximum current for flash mode
+          is hardwired to the component using the RFS resistor to
+          ground. The maximum hardware current setting is calculated
+          according to the formula Imax = 5500 / RFS. The lowest
+          allowed resistance value is 7.86 kOhm giving an absolute
+          maximum current of 700mA. By setting this attribute in
+          the device tree, you can further restrict the maximum
+          current below the hardware limit. This requires the RFS
+          to be defined as it defines the maximum range.
+
+      led-max-microamp:
+        maximum: 700000
+        description: The maximum current for torch mode
+          is hardwired to the component using the RTS resistor to
+          ground. The maximum hardware current setting is calculated
+          according to the formula Imax = 5500 / RTS. The lowest
+          allowed resistance value is 7.86 kOhm giving an absolute
+          maximum current of 700mA. By setting this attribute in
+          the device tree, you can further restrict the maximum
+          current below the hardware limit. This requires the RTS
+          to be defined as it defines the maximum range.
+
+    additionalProperties: false
+
+required:
+  - compatible
+  - ent-gpios
+  - enf-gpios
+  - led
+
+additionalProperties: false
+
+examples:
+  - |
+    #include <dt-bindings/gpio/gpio.h>
+    #include <dt-bindings/leds/common.h>
+
+    led-controller {
+        compatible = "richtek,rt8515";
+        enf-gpios = <&gpio4 12 GPIO_ACTIVE_HIGH>;
+        ent-gpios = <&gpio4 13 GPIO_ACTIVE_HIGH>;
+        richtek,rfs-ohms = <16000>;
+        richtek,rts-ohms = <100000>;
+
+        led {
+            function = LED_FUNCTION_FLASH;
+            color = <LED_COLOR_ID_WHITE>;
+            flash-max-timeout-us = <250000>;
+            flash-max-microamp = <150000>;
+            led-max-microamp = <25000>;
+        };
+    };
+
+...