docs(backlight): improve documentation

docs/docs/features/backlight.md

@@ -3,19 +3,20 @@ title: Backlight
 sidebar_label: Backlight
 ---
 
+import Tabs from '@theme/Tabs';
+import TabItem from '@theme/TabItem';
+
 Backlight is a feature used to control array of LEDs, usually placed through or under switches. Unlike [RGB Underglow](underglow.md), backlight currently allows only one color per LED, also LEDs are not addressable, so you can't control individual LEDs.
 
 ## Enabling Backlight
 
-To enable backlight on your board or shield, add the following lines to your `.conf` file of your user config directory as such:
+To enable backlight on your board or shield, add the following line to your `.conf` file of your user config directory as such:
 
 ```
-CONFIG_PWM=y
-CONFIG_LED_PWM=y
 CONFIG_ZMK_BACKLIGHT=y
 ```
 
-If your board or shield does not have backlight configured, refer to [Adding Backlight to a Board](#adding-backlight-to-a-board).
+If your board or shield does not have backlight configured, refer to [Adding Backlight to a board or a shield](#adding-backlight-to-a-board-or-a-shield).
 
 ## Configuring Backlight
 
@@ -29,13 +30,31 @@ There are various Kconfig options used to configure the backlight feature. These
 | `CONFIG_ZMK_BACKLIGHT_AUTO_OFF_IDLE` | Turn off backlight when keyboard goes into idle state | n       |
 | `CONFIG_ZMK_BACKLIGHT_AUTO_OFF_USB`  | Turn off backlight when USB is disconnected           | n       |
 
-## Adding Backlight to a Board
+## Adding Backlight to a board or a shield
+
+<Tabs
+defaultValue="shield"
+values={[
+{label: 'Adding to a board', value: 'board'},
+{label: 'Adding to a shield', value: 'shield'},
+]}>
+<TabItem value="board">
+
+First, you must enable PWM by adding the following lines to your `Kconfig.defconfig` file:
+
+```
+if ZMK_BACKLIGHT
 
-Backlight is always added to a board, not a shield.
-If you have a shield with backlight, you must add a `boards/` directory within your shield folder to define the backlight individually for each board that supports the shield.
-Inside the `boards/` folder, you define a `<board>.overlay` for each different board.
+config PWM
+    default y
 
-First, you need to enable PWM by adding the following lines to your `.overlay` file:
+config LED_PWM
+    default y
+
+endif # ZMK_BACKLIGHT
+```
+
+Then you have to add the following lines to your `.dts` file:
 
 ```
 &pwm0 {
@@ -52,14 +71,17 @@ For example, _P1.13_ would give you _32 \* 1 + 13_ = `<45>` and _P0.15_ would gi
 
 If your board uses a P-channel MOSFET to control backlight instead of a N-channel MOSFET, you may want to enable `ch0-inverted`.
 
-Then you have to add the following lines to your `.dtsi` file inside the root devicetree node:
+Then you have to add the following lines inside the root devicetree node on the same file as before:
 
 ```
+/ {
     backlight: pwmleds {
         compatible = "pwm-leds";
         label = "Backlight LEDs";
         pwm_led_0 {
             pwms = <&pwm0 45>;
+        	label = "Backlight LED 0";
+        };
     };
 };
 ```
@@ -73,12 +95,100 @@ Note that every LED inside of the backlight node will be treated as a backlight
 Finally you need to add backlight to the `chosen` element of the root devicetree node:
 
 ```
+/ {
+    chosen {
+        zmk,backlight = &backlight;
+    };
+}:
+```
+
+</TabItem>
+<TabItem value="shield">
+
+You must first add a `boards/` directory within your shield folder. For each board that supports the shield you must create a `<board>.defconfig` file and a `<board>.overlay` file inside the `boards/` folder.
+
+Inside your `<board>.defconfig` file, add the following lines:
+
+```
+if ZMK_BACKLIGHT
+
+config PWM
+    default y
+
+config LED_PWM
+    default y
+
+endif # ZMK_BACKLIGHT
+```
+
+Then add the following lines to your `.overlay` file:
+
+```
+&pwm0 {
+	status = "okay";
+	ch0-pin = <45>;
+	/* ch0-inverted; */
+};
+```
+
+The value `ch0-pin` represents the pin that controls the LEDs. With nRF52 boards, you can calculate the value to use in the following way: you need the hardware port and run it through a function.
+**32 \* X + Y** = `<Pin number>` where X is first part of the hardware port "PX.01" and Y is the second part of the hardware port "P1.Y".
+
+For example, _P1.13_ would give you _32 \* 1 + 13_ = `<45>` and _P0.15_ would give you _32 \* 0 + 15_ = `<15>`.
+
+If your shield uses a P-channel MOSFET to control backlight instead of a N-channel MOSFET, you may want to enable `ch0-inverted`.
+
+Then you have to add the following lines inside the root devicetree node on the same file:
+
+```
+/ {
+    backlight: pwmleds {
+        compatible = "pwm-leds";
+        label = "Backlight LEDs";
+        pwm_led_0 {
+            pwms = <&pwm0 45>;
+        	label = "Backlight LED 0";
+        };
+    };
+};
+```
+
+The value inside `pwm_led_0` must be the same as you used before.
+
+:::info
+Note that every LED inside of the backlight node will be treated as a backlight LED, so if you have other PWM LEDs you need to declare them in a separate node. Refer to [Multiple backlight LEDs](#multiple-backlight-leds) if you have multiple backlight LEDs.
+:::
+
+Finally you need to add backlight to the `chosen` element of the root devicetree node:
+
+```
+/ {
     chosen {
-    ...
         zmk,backlight = &backlight;
     };
+}:
 ```
 
+Optionally, on Pro Micro compatible shields you can add a LED GPIO node to your devicetree, this could be useful if you want your shield to be compatible with newer or untested boards. To do that you have to enable `CONFIG_LED_GPIO` in your `.conf` file and then add the following lines inside the root devicetree node of your `.dtsi` or `.dts` file:
+
+```
+/ {
+    backlight: gpioleds {
+        compatible = "gpio-leds";
+        label = "Backlight LEDs";
+        gpio_led_0 {
+            gpios = <&pro_micro 20 GPIO_ACTIVE_HIGH>;
+        	label = "Backlight LED 0";
+        };
+    };
+};
+```
+
+If no suitable `<board>.overlay` file is found, this node will act as a fallback, however, without PWM, backlight has limited functionality.
+
+</TabItem>
+</Tabs>
+
 ### Multiple backlight LEDs
 
 It is possible to control multiple backlight LEDs at the same time. This is useful if, for example, you have a Caps Lock LED connected to a different pin and you want it to be part of the backlight.