Re: [Buildroot] [PATCH 2/2] configs/aarch64_efi: support net boot with devicetree

[Julien Olivain via buildroot <buildroot@buildroot.org>]

Hi Vincent,

On 17/06/2026 19:10, Vincent Stehlé wrote:
> UEFI platforms with a Devicetree have recently gained support for some 
> form
> of network booting. [1][2]
> 
> On those platforms, the UEFI firmware downloads the disk image over the
> network and presents it to UEFI applications using the simple 
> filesystem
> protocol. This is sufficient for OS loaders such as e.g. GRUB to find 
> their
> configuration and load the kernel image.
> 
> The firmware must also describe the ramdisk to the OS, so that it finds 
> its
> root filesystem. On ACPI based platforms this is done with an NVDIMM
> Firmware Interface Table (NFIT). On Devicetree based platforms, this 
> can be
> done with a pmem node. [3]
> 
> Add a kernel config fragment to add pmem support, which enables network
> boot on UEFI platforms with Devicetree.
> Also, briefly mention that we support this scenario in the readme.
> 
> This can be tested on Qemu, with the following procedure:
> 
> Build aarch64_efi_defconfig in a folder, to obtain 
> output/images/disk.img,
> and serve the image over HTTP with python:
> 
>   $ python -m http.server -d output/images/
> 
> In another terminal and another folder, configure a U-Boot based 
> firmware
> starting from qemu_aarch64_ebbr_defconfig, and with the following
> additional configurations:
> 
>   BR2_TARGET_UBOOT_CUSTOM_VERSION_VALUE="2026.04"
>   BR2_TARGET_UBOOT_NEEDS_DTC=y
> 
> Add the following U-Boot configurations to
> board/qemu/aarch64-ebbr/u-boot.fragment:
> 
>   CONFIG_EFI_HTTP_BOOT=y
>   CONFIG_NET_LWIP=y

Maybe those config changes in qemu_aarch64_ebbr_defconfig and
board/qemu/aarch64-ebbr/u-boot.fragment you are mentioning here
could be included in a followup update of qemu_aarch64_ebbr_defconfig.
What do you think?

If you do so, you could probably add a small section in
board/qemu/aarch64-ebbr/readme.txt
quickly describing this new capability, same as you did here.

> Build everything; you should obtain output/images/flash.bin.
> 
> Start Qemu as per board/qemu/aarch64-ebbr/readme.txt, but omitting the 
> hd0
> -device and -drive stanzas.
> U-Boot should start; interrupt it with enter.
> 
> At U-Boot prompt, type the following commands:
> 
>   => setenv loadaddr 0x43000000
>   => efidebug boot rm 0

While testing, this comment reported a message that looked like an 
error:

     => efidebug boot rm 0
     Cannot persist EFI variables without system partition
     Missing TPMv2 device for EFI_TCG_PROTOCOL
     Cannot remove Boot0000

But the whole sequence successfully booted the aarch64 efi image.

Is this command really needed?

>   => efidebug boot add -u 0 net http://10.0.2.2:8000/disk.img
>   => efidebug boot order 0
>   => bootefi bootmgr
> 
> U-Boot should download the disk image over HTTP and boot Linux with 
> UEFI.
> Look for the following message in Linux boot log, to confirm that it 
> did
> indeed mount its rootfs from the downloaded image:
> 
>   EXT4-fs (pmem0p2): mounted filesystem ...
> 
> Link: 
> https://www.linaro.org/blog/installing-fedora-with-uefi-http-boot/ [1]
> Link: 
> https://docs.u-boot-project.org/en/latest/develop/uefi/uefi.html#uefi-http-boot-using-the-legacy-tcp-stack 
> [2]
> Link: 
> https://github.com/ARM-software/edge-iot-arch-guide/blob/main/source/http-boot/pmem_node.md 
> [3]
> Signed-off-by: Vincent Stehlé <vincent.stehle@arm.com>
> Cc: Dick Olsson <hi@senzilla.io>

Best regards,

Julien.
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