[U-Boot] [U-Boot, v7, 2/2] arm: move gd handling outside of C code

[Stephen Warren <swarren@wwwdotorg.org>]

On 01/14/2016 12:11 PM, Tom Rini wrote:
> On Thu, Jan 14, 2016 at 11:35:39AM -0700, Stephen Warren wrote:
>> On 01/14/2016 06:20 AM, Tom Rini wrote:
>>> On Wed, Nov 25, 2015 at 05:56:33PM +0100, Albert ARIBAUD wrote:
>>>
>>>> As of gcc 5.2.1 for Thumb-1, it is not possible any
>>>> more to assign gd from C code, as gd is mapped to r9,
>>>> and r9 may now be saved in the prolog sequence, and
>>>> restored in the epilog sequence, of any C functions.
>>>>
>>>> Therefore arch_setup_gd(), which is supposed to set
>>>> r9, may actually have no effect, causing U-Boot to
>>>> use a bad address to access GD.
>>>>
>>>> Fix this by never calling arch_setup_gd() for ARM,
>>>> and instead setting r9 in arch/arm/lib/crt0.S, to
>>>> the value returned by board_init_f_alloc_reserve().
>>>>
>>>> Signed-off-by: Albert ARIBAUD <albert.u.boot@aribaud.net>
>>>> Reviewed-by: Simon Glass <sjg@chromium.org>
>>>
>>> Applied to u-boot/master, thanks!
>>
>> FYI, this commit causes U-Boot to fail (crash or hang during very
>> early startup with zero UART output) on at least an NVIDIA Jetson
>> TX1 (p2371-2180) board. Reverting just this in u-boot/master solves
>> the issue. I have not tested other boards or looked at the code
>> itself yet.
>
> Is that one of the systems where we have an ARM9 and then a Cortex-A?
> FWIW, my pandaboard is up in Fedora currently.  I'm trying to do some
> boot testing on what I have more often and then a bigger round of
> unboxing and testing at -rc1/release time.

This board is AArch64. There's no SPL or dual-architecture U-Boot on 
this system; a boot CPU runs the boot ROM and and NVIDIA binary 
bootloader which loads U-Boot from disk and sets up the main CPU, then 
the main ARM CPU essentially jumps straight into the main U-Boot binary.

For more precise details, see:

ftp://download.nvidia.com/tegra-public-appnotes/t210-nvtboot-flow.html

or a bunch of stuff accessible from the following for more background:

ftp://download.nvidia.com/tegra-public-appnotes/index.html