Chainloading U-Boot from Fastboot on Tegra30

[Tom Rini]

On Fri, Aug 21, 2020 at 05:30:54PM -0400, Peter Geis wrote:
> On Fri, Aug 21, 2020 at 5:04 PM Tom Rini <trini at konsulko.com> wrote:
> >
> > On Fri, Aug 21, 2020 at 04:17:24PM -0400, Peter Geis wrote:
> > > On Mon, Jul 6, 2020 at 3:48 PM Peter Geis <pgwipeout at gmail.com> wrote:
> > > >
> > > > On Mon, Jul 6, 2020 at 1:04 PM Stephen Warren <swarren at wwwdotorg.org> wrote:
> > > > >
> > > > > On 7/3/20 6:32 AM, Peter Geis 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 assume that fastboot executes the loaded code on the main CPU not on
> > > > > the boot CPU (AVP). U-Boot SPL on Tegra30 expects to start running on
> > > > > the AVP though; you would have to disable SPL to make this all work, and
> > > > > perhaps fix U-Boot to work without SPL present. I'm not sure what, if
> > > > > any, changes would be required to support that.
> > > > >
> > > > > For background, see:
> > > > > https://http.download.nvidia.com/tegra-public-appnotes/index.html
> > > >
> > > > Apologies for the resend, I realized I didn't reply to the list.
> > > >
> > > > I admit I'm still extremely new to U-Boot, but this is the way I
> > > > understand the boot flow.
> > > > ROM does extremely low level init, then loads U-boot SPL.
> > > > U-Boot SPL does basic init, ram, cpu and required peripherals, then
> > > > loads U-Boot.bin.
> > > > U-Boot.bin is U-Boot proper, with the full interface.
> > > >
> > > > By loading U-Boot.bin as the nyan instructions indicated, I'm
> > > > bypassing the SPL code as if it was already complete.
> > > > The issue I have is I'm not sure what modifications were done to the
> > > > T124 code to allow nyan to do this.
> > > > I've compared the nyan configs to the cardhu configs and I don't see
> > > > anything that sticks out to me.
> > > > I've also dug through the nyan git log and I don't see anything that
> > > > was specifically changed to allow chainloading on T124.
> > > >
> > > > I also am unsure of where fastboot is loading the kernel in order to
> > > > set the text base correctly.
> > >
> > > For anyone interested, I succeeded at chainloading u-boot on the Ouya.
> >
> > Nice work.
> >
> > > The Linux Kernel with low level debugging enabled in the decompressor
> > > will print the load address.
> > >
> > > Jumping to kernel at:4861 ms
> > >
> > > C:0x80A000C0-0x8112BA40->0x8152C700-0x81C58080
> > > Uncompressing Linux...
> > >
> > > So by setting the u-boot text base to 0x80A00000 u-boot now executes,
> > > but it would then immediately silently reboot.
> > > Turns out I needed to define the console in the device-tree, which
> > > isn't defined in the u-boot tegra30-cardhu.dts.
> > > It would then freeze at relocation time, as it was trying to overwrite
> > > the trustzone ram space.
> > > #define CONFIG_PRAM 2048 solves that issue.
> > >
> > > I'd like to know if u-boot can read the reserved-memory device-tree
> > > node and use it instead of CONFIG_PRAM?
> >
> > Honestly, this is what CONFIG_PRAM is for.  We could possibly add
> > something to get this from device-tree, but we might need to do that
> > early enough that it becomes a tricky thing to do.
> 
> Thank you, that makes sense.
> 
> >
> > > Otherwise the only issue it seems to have it is does not read the
> > > nvidia proprietary partition table.
> > > Is there a way to force u-boot to read the backup gpt table similar to
> > > the android kernel's method?
> >
> > Some tangential experiments the other day and I saw that U-Boot would
> > read the backup GPT if it's at the expected place.  But that might be
> > only after you do something like "part list mmc 0", so there might in
> > turn be places that we need to be a bit more robust in our checking.
> 
> Unfortunately running <part list mmc 0> returns "## Unknown partition
> table type 0"
> 
> This is the result of the gpt guid command:
> Tegra30 (Ouya) # gpt guid mmc 0
> GUID Partition Table Header signature is wrong: 0x1000 != 0x5452415020494645
> find_valid_gpt: *** ERROR: Invalid GPT ***
> find_valid_gpt: ***        Using Backup GPT ***
> 00000000-0000-0000-0000-000000000000
> success!
> 
> The backup GPT is a valid GPT, and linux will pull the partition table
> from it if forced to look there.
> The android kernel handled this by adding "gpt gpt_sector=15073279" to
> the command line.

Ah, interesting.  And where is that sector in relation to where the
backup should be?  I'm not sure off-hand how easy it would be to make
backup location easy to run-time configure, but if it's lba - 2 instead
of lba - 1 or something, we could add a build-time "also check.." thing,
if it's a consistent offset, and probably is.  Similarly, we could add
something kinda ugly to allow overriding GPT_PRIMARY_PARTITION_TABLE_LBA
with where that is instead.

Other-otherwise, I know there's patches in progress to support "tegra
partition table" for Linux and doing that for U-Boot could be handy and
fix this problem as well?

-- 
Tom
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