Where does the DTB file get loaded from during UEFI boot?

[pengyang1]

When UEFI starts up, it specifies the paths to the kernel, initrd, and dtb in the configuration file extlinux.conf located in the APP partition.
However, if the dtb path is not specified in this file, no relevant logic is found in the code, where is the dtb obtained from?

[KevinFFF]

Hi pengyang1,

@pengyang1

However, if the dtb path is not specified in this file, no relevant logic is found in the code, where is the dtb obtained from?

It will be loaded from partition.
Please refer to UEFI Adaptation — DTB Support for the workflow of DTB loading.

[pengyang1]

Kevin:
Thank you for your reply—it’s very clear.
According to the flowchart, if we choose the kernel from the rootfs via extlinux.conf, and there is no FDT entry in extlinux.conf, the UEFI DTB will be selected.
Will the DTB be bound to the UEFI during compilation?

[KevinFFF]

@pengyang1

Will the DTB be bound to the UEFI during compilation?

Yes, it is handled by the flash script and generated during flash.
(i.e. uefi_t26x_general_with_dtb.bin)

Please also note the following lines in board config(i.e. jetson-agx-thor-devkit.conf)

DTB_FILE="tegra264-p4071-0000+p3834-0008-nv.dtb";
TBCDTB_FILE="${DTB_FILE}";

DTB_FILE is the device tree used by kernel while TBCDTB_FILE is the device tree used by UEFI.
They use the similar DTB file by default.