[U-Boot] [PATCH] p2371-2180: Build position independent binary

[Stephen Warren]

On 3/19/19 6:12 AM, Thierry Reding wrote:
> On Mon, Mar 18, 2019 at 12:31:32PM -0600, Stephen Warren wrote:
>> On 3/8/19 1:10 PM, Thierry Reding wrote:
>>> From: Thierry Reding <treding at nvidia.com>
>>>
>>> In order to support chainloading of U-Boot by an earlier bootloader,
>>> make sure the binary is position independent, so that the earlier boot-
>>> loader can relocate it if necessary.
>>
>> Why not enable this for all 64-bit Tegra? They're all booted the exact same
>> way at least with recent L4T builds.
> 
> Yeah, I think that would make sense.
> 
>> Also, U-Boot is typically linked to the address that cboot loads it to, and
>> cboot typically always loads to precisely that address. I'm not sure why
>> this patch is required.
> 
> I encountered this issue when I was trying to chainload U-Boot from
> cboot on Jetson TX1. It seems like your above comment is no longer true,
> though I suppose that could just mean that the link address for U-Boot
> has become stale?

Looks like the upstream CONFIG_SYS_TEXT_BASE is indeed stale relative to 
the latest L4T builds:

Upstream:
Jetson TX1: CONFIG_SYS_TEXT_BASE=0x80110000
Jetson TX2: CONFIG_SYS_TEXT_BASE=0x80080000

L4T r32.1:
Jetson TX1: #define CONFIG_SYS_TEXT_BASE    0x80080000
Jetson TX2: #define CONFIG_SYS_TEXT_BASE    0x80080000

>> That said, it don't think it harms anything, so I'm fine with it being
>> applied.
> 
> I suppose there's a bit of extra code to do the indirect jumps, but
> overall U-Boot seems to work well and not noticeably slower if this is
> enabled. Might be nice for extra flexibility and to avoid any surprises
> if we ever end up loading U-Boot to a location other than where it was
> liked to.
> 
> My understanding is that this could happen on Tegra186 if cboot detects
> bad memory blocks in the area where U-Boot was meant to be loaded to. I
> guess this doesn't apply to earlier chips, but perhaps it's good to have
> it there for consistency anyway.

Yes, this could happen on Jetson TX2i at least.