barebox for a ti am335x based board

[Sascha Hauer]

Hi Giorgio,

On Tue, Feb 13, 2018 at 11:12:54PM +0100, Giorgio Dal Molin wrote:
> Hi all,
> 
> I'm trying to add board code for an am335x based HW project.
> I had a look at similar boards like 'boards/phytec-som-am335x'
> or 'boards/beaglebone'.
> I understand that I need two images: the (little) MLO and the
> (bigger) barebox.
> 
> What it's not really clear is how the MLO loads and starts the
> barebox.

See arch/arm/mach-omap/xload.c. It is compiled when no shell is enabled
(I think at least for clarity there should be a separate Kconfig
symbol). In this file omap_xload() detects where the SoC has booted from
and loads the full barebox from the same source.

> 
> Moreover I saw there's always a call to:
> 
>  am33xx_save_bootinfo((void *)bootinfo);
> 
> in the MLO lowlevel entry function; I suspect the argument
> 'bootinfo' is the register r0 left by the function __barebox_arm_head()
> but I cannot really understand the logic behind it.

When the am335x ROM passes control to the bootloader then it passes in
R0 a pointer to the bootinfo. This is a three word structure which has
informations where the SoC has booted from. In am33xx_save_bootinfo() we
copy the information to a known place where we can pick it up later, see
am33xx_bootsource().

Sascha


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