====== Android Device Tree Overlay ======

We can use DT overlays to enable/disable or change the configuration of peripherals without recompiling the kernel source code.

===== Device Reference Table ======

^         ^  Android Version  ^  DT overlays folder                                                  ^  DT overlays list variable  ^  DT overlays config file                                                       ^
^  Edge2  |  14               |  /vendor/custom/boot/dtb/rockchip/rk3588s-khadas-edge2.dtb.overlays  | fdt_overlays                |  /vendor/custom/boot/dtb/rockchip/rk3588s-khadas-edge2.dtb.overlay.env         |
^  VIM4   |  11,14            |  /mnt/vendor/odm_ext/custom/overlays/kvim4.dtb.overlays              | fdt_overlays                |  /mnt/vendor/odm_ext/custom/overlays/kvim4.dtb.overlays/kvim4.dtb.overlay.env  |


===== Device Configurations =====


<tabbox Edge2 >

DT-overlays ''dtbo'' directory: ''/vendor/custom/boot/dtb/rockchip/rk3588s-khadas-edge2.dtb.overlays''

```shell
khadas@Khadas:~$ ls vendor/custom/boot/dtb/rockchip/rk3588s-khadas-edge2.dtb.overlays
edge2-io-spi.dtbo
```

DT-overlays configuration file: ''/mnt/vendor/odm_ext/custom/overlays/kvim4.dtb.overlays/kvim4.dtb.overlay.env''

Enable：
```shell
$ echo fdt_overlays=edge2-io-spi > /vendor/custom/boot/dtb/rockchip/rk3588s-khadas-edge2.dtb.overlay.env
```
```shell
$ cat rk3588s-khadas-edge2.dtb.overlay.env
fdt_overlays=edge2-io-spi

```

Disable：
```shell
$ echo fdt_overlays= > /vendor/custom/boot/dtb/rockchip/rk3588s-khadas-edge2.dtb.overlay.env
```
```shell
$ cat rk3588s-khadas-edge2.dtb.overlay.env
fdt_overlays=

```

<tabbox VIM4>
DT-overlays ''dtbo'' directory: ''/mnt/vendor/odm_ext/custom/overlays/kvim4.dtb.overlays''.

```shell
khadas@Khadas:~$ ls -1 /mnt/vendor/odm_ext/custom/overlays/kvim4.dtb.overlays
i2s.dtbo  
pwm_f.dtbo  
spdifout.dtbo  
uart_e.dtbo
```
DT-overlays configuration file: ''/mnt/vendor/odm_ext/custom/overlays/kvim4.dtb.overlay.env''

Enable：
```shell
$ echo fdt_overlays=i2s > /mnt/vendor/odm_ext/custom/overlays/kvim4.dtb.overlay.env
```
```shell
$ cat kvim4.dtb.overlay.env
fdt_overlays=i2s

```

Disable：
```shell
$ echo fdt_overlays= > /mnt/vendor/odm_ext/custom/overlays/kvim4.dtb.overlay.env
```
```shell
$ cat kvim4.dtb.overlay.env
fdt_overlays=

```
</tabbox>

===== Configuration DT Overlays =====

You need to edit the DT overlays configuration file and add custom DT overlays dtbo files to a special folder.

===== Make custom DT Overlays =====

There are some preparation steps for DT overlays dtbo files, you can also add custom DT overlays.

==== Write DT Overlay Source====

Basic  DT overlay source example:

```dts example.dts 
/dts-v1/;
/plugin/;

/ {
    fragment@0 {
        target = <&i2c3>;
        __overlay__ {
            status = "disabled";
        };
    };
};
```

==== Compile DT Overlay Source ====

```sh
dtc -I dts -O dtb -o example.dtbo example.dts
```


===== Reboot =====

Need reboot board to take effect.