How to use self created device tree overlays for component deactivation

[Sebastian 0]

Good morning,

I am working with the Tinker Board S for a customer project and need to deactivate components for production as a security and perfomance measure. 

For example, I want to deactivate the GPU and and WiFi via device tree overlays as a low level approach to accomplish this goal. I saw that you shiped several overlays and found a couple of entries in this forum about overlays making me believe that this is the approach to go. Unfortunately, I was not able to succeed so far. 

What I did:

1. tested to compile the three attached overlays.

compilation with 
dtc -O dtb -o disable-gpu.dtbo -b 0 -@ disable-gpu-overlay.dts 
worked fine.

I move the file disable-gpu.dtbo to /boot/overlays and added them at the end of /boot/config.txt (overlay=disable-gpu)

but the overlay seems not to be loaded, because GPU and Desktop still booting and: 
dmesg | grep -i overlay 
returns nothing -> no overlays loaded

2. Next approach was to load it manually, but "dtoverlay" is not installed (should be included into device-tree-compiler package)

3. As an alternative I wanted to decompile the dtb and change the activation status directly there or apply the overlays manually to the dtb. But I do not find any *.dtb file in the filesystem. 

Could you please point me to the best way to accomplish my overall goal and walk me through the process?

Thank you in advance!

disable-gpu-overlay_approach1.dts disable-gpu-overlay_approach2.dts disable-gpu-overlay_approach3.dts deviceTreeOutput.txt config.txt

[tooz 56]

hello @Sebastian, 

to compile the dtbo: 

dtc -@ -O dtb -o disable-gpu-wifi.dtbo disable-gpu-wifi.dts

(or, you can download the dts & dtbo from this link )

once you have the dts and dtbo, move them to the /boot/overlays and modify the config.txt

cp disable-gpu-wifi.dtbo /boot/overlays/
sudo vim /boot/config.txt
overlay=disable-gpu-wifi
sudo reboot

to verify that gpu is disabled: 

check if the directory /sys/devices/platform/ffa30000.gpu/ exists; if it's non existent = gpu is disabled 

 this is what in the disable-gpu-wifi.dts: 

/dts-v1/;

/plugin/;

 

/ {

    compatible = "rockchip,rk3288";

 

    fragment@0 {

        target = <&gpu>;

        __overlay__ {

            status = "disabled";

        };

    };

   

    fragment@1 {

        target-path = "/wireless-wlan";

        __overlay__ {

            status = "disabled";

        };

    };

};

 

[Sebastian 0]

Hello @tooz

Thank you very much for your support. I was able to build the dtbo file and apply the overlay successfully. Actually, what really helped me was to understand how I validate the deactivation by evaluating the existance of /sys/devices/platform/ffa30000.gpu. (and /sys/devices/platform/wireless-wlan resp.)

dmesg | grep -i overlay 

still returns nothing, even when the overlay is successfully applied. With this knowledge I re-evaluated my former dts files - the first one already worked.

Once again: Thanks. This helped me to solve my issue.

Edited March 25, 2025 by Sebastian