Chainloading U-Boot from Fastboot on Tegra30

[Simon Glass]

Hi Peter,

On Sun, 5 Jul 2020 at 05:33, Peter Geis <pgwipeout at gmail.com> wrote:
>
> 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?

Yes, so long as you know the address. Is the MMU turned off? Cache?

>
> >
> > 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.

OK. Maybe there is someone on this list with a bit more Android
booting experienec?

>
> 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

OK, I'm sure it is possible. Do you have the source code for the
fastboot code that boots U-Boot?

Regards,
Simon