How to build U-Boot with a custom out-of-tree device tree

[Johannes Krottmayer]

Hi Simon!

Thanks for your answer.

On 4/20/26 2:51 AM, Simon Glass wrote:
> Hi Johannes,
> 
> On Sun, 19 Apr 2026 at 02:40, Johannes Krottmayer <krotti83 at proton.me> wrote:
>>
>> Hello,
>>
>> This question is generic and also valid for none RISC-V boards.
>> I think it's maybe already asked, but didn't find any useful
>> information this time. My question is, is it possible to pass
>> a specific device tree blob to the build system from U-Boot?
>>
>> Example: RISC-V board Starfive VisionFive 2 8GiB variant
>>
>> The default in-source-tree device tree from the VisionFive 2 has
>> only 4GiB RAM. I own the 8GiB (RAM-IC BiWin BMWZCX32H2A-64G-X)
>> variant. So therefore can I pass the device tree blob directly
>> to U-Boot's build system without modifying CONFIG_DEFAULT_DEVICE_TREE
>> in the device configuration? Exists there an environment variable?
>>
>> Want to use U-Boot's EFI subsystem as loader for bare-metal
>> environments. And I think when I want to get the
 memory map
>> via EFI there will with the default device tree only <4GiB free
>> usable memory shown, although there are 8GiB.
> 
> You can build with: make DEVICE_TREE=...
> 
> See dts/Makefile for the logic.
> 

Didn't figured out how it works with the variable DEVICE_TREE
yet.

But I found the variable EXT_DTB in your described Makefile.
Have tried it now with a precompiled device tree and it works
fine.

make EXT_DTB=/path/to/custom_board.dtb

>>
>> Thanks in advance!
>>
>> Kind regards,
>>
>> Johannes K.
> 
> Regards,
> Simon

Kind regards,

Johannes K.
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