From mboxrd@z Thu Jan  1 00:00:00 1970
From: Stephen Warren <swarren@wwwdotorg.org>
Date: Tue, 16 Feb 2016 09:41:36 -0700
Subject: [U-Boot] how does board_init_f() -> board_init_r?
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On 02/16/2016 09:01 AM, Simon Glass wrote:
> +Stephen who will know more
>
> Hi,
>
> On 13 February 2016 at 18:52, quantumlight <peter.feifan.chen@gmail.com> wrote:
>> I am trying to modify the bootloader code for NVIDIA's jetson board.
>>
>> So I am looking at crt0.S. It seems that two builds happen, one with
>> CONFIG_SPL_BUILD and one without. So you end up with two file, u-boot.bin
>> and spl/u-boot-spl.bin.
>
> SPL is built with ARMv4t
> U-Boot proper is built with ARMv7
>
> That's why SPL is used on Tegra. The SPL does not actually load
> U-Boot. In fact both are bundle together and loaded at the same time.
> SPL simply jumps to U-Boot when needed.

There's some more background on this topic at:

ftp://download.nvidia.com/tegra-public-appnotes/index.html

In particular, see the "Tegra Boot Flow" link/document.