[U-Boot] how does board_init_f() -> board_init_r?

[Simon Glass]

+Stephen who will know more

Hi,

On 13 February 2016 at 18:52, quantumlight <peter.feifan.chen at 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.

>
> However, I am unable to find the code path that calls board_init_r() after
> board_init_f() finishes, although there are several candidates:
>
> 1) crt0.S - if CONFIG_SPL_BUILD was not defined, then it would fall straight
> through to board_init_r() - HOWEVER, for u-boot.bin, isn't CONFIG_SPL_BUILD
> defined in autoconf.h? Or is this some clever magic between how u-boot.bin
> and spl/u-boot-spl.bin are stitched together?

For U-Boot, CONFIG_SPL_BUILD is not defined. That define means you are
building SPL.

The clever magic is mostly 'cat'. SPL is padded a little and then
U-Boot is added on the end.

> 2) _weak board_init_f in arch/arm/lib/spl.c - HOWEVER, shouldn't this be
> overloaded by board_init_f in common/board_f.c?

The latter is only used in U-Boot proper. SPL has its own board_init_f().

> 3) board_init_f_r in common/board_f.c - HOWEVER, nothing calls
> board_init_f_r().

No, that is not used on ARM.

>
> Can someone illuminate me on how this happens?
>

See the README under Board Initialisation Flow. In brief, the link
between board_init_f() and board_init_r() is generally the crt0.S that
you found. The catch is that some boards don't implement
board_init_f() in SPL, and so use the weak one, which in fact calls
board_init_r() directly.

See also arch/arm/mach-tegra/board.c which I think contains the code
to jump to SPL.

Regards,
Simon