Chainloading U-Boot from Fastboot on Tegra30

[Peter Geis]

On Sat, Jul 4, 2020 at 3:53 PM Simon Glass <sjg at chromium.org> wrote:
>
> Hi Peter,
>
> On Fri, 3 Jul 2020 at 06:33, Peter Geis <pgwipeout at gmail.com> wrote:
> >
> > Good Morning,
> >
> > I am attempting to expand on the work for chainloading U-Boot on the
> > nyan-big in order to chainload U-Boot on the Ouya Tegra30 device from fastboot.
> > I have so far been unsuccessful at getting any output from U-Boot
> > through this method.
> >
> > I'm building the cardhu board with tweaks for Ouya's specifications
> > similar to my work for the linux kernel.
> > I build the image using mkbootimg --kernel u-boot.bin --ramdisk
> > /dev/null --output u-boot-android.bin.
> > I then fastboot boot u-boot-android.bin.
> >
> > I've tried tweaking the text base and tried both standard debug and
> > low level debug.
> >
> > Do you think you could give me some insight into where I'm going wrong?
>
> Is it possible that fastboot expects a relocatable image? If you set
> up the debug UART very early you might be able to output a character
> in start.S ?

Yes, fastboot expects a relocatable image.
As I understand it though, if I get the text base correct, U-boot will
not need to relocate.

The debug UART is already set up when it fastboot jumps to the loaded kernel,
So I should be able to dump data to the expected raw address and it
will show up?

>
> BTW does U-Boot have support for the fastboot protocol? Perhaps you
> could just use U-Boot?

The Ouya is locked with a signed boot loader, like most consumer
android devices.
Unlike most other devices, it does not have a hardware method for
entering the bootloader in case of a brick.
We are currently using a hacked kernel that stores another kernel in
"safe" ram via kexec and hard resets the board, but a proper
bootloader would be much more preferable.

I found one example of where fastboot chainloaded u-boot successfully
on the galaxy nexus, from 2013.
https://forum.xda-developers.com/galaxy-nexus/bootloader-boot-multi-boot-support-t2201146

>
> Regards,
> Simon