Which booti operations are essential when booting Linux directly from TF-A?

[Joita Mitra]

Hi,
I am investigating a direct Linux boot flow where ARM Trusted Firmware (TF-A) transfers control directly to Linux instead of booting U-Boot first.
Current flow:

BL2 -> BL31 -> U-Boot -> Linux

Target flow:

BL2 -> BL31 -> Linux

While studying the ARM64 boot flow in U-Boot, I examined:

cmd/booti.c
boot/bootm.c
boot/bootm_os.c

and observed that U-Boot performs significantly more work than simply jumping to the kernel entry point.
To replicate the required functionality inside TF-A, I am trying to identify which steps are essential.
Could you please clarify:

  1.  Which parts of the booti flow are mandatory before entering an ARM64 Linux kernel?
  2.
If Linux is already loaded at its final execution address, which parts of booti can safely be skipped?
  3.  Are there any minimal examples showing the required state that Linux expects when entered from firmware instead of U-Boot?

My goal is to reproduce only the minimum required Linux preparation steps inside TF-A.
At this stage, the most important unanswered question is not how to jump to Linux, but what exact environment U-Boot creates that Linux depends on.
Any pointers to the relevant source files or functions would be greatly appreciated.
Thank you.





[cid:9b7d87bd-47e2-45f8-aadf-b22a57c6c945]<http://www.delopt.co.in/>

Joita Mitra

Embedded Software Engineer

[cid:662cd72c-cb0a-4938-9038-6d7ccf6966d7] +91-7985313796

Fortune Serene, 3rd Floor, Plot No: 89/B, 90/A, West Avenue 9, Electronic City Phase 1,Bangalore 560100


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