[U-Boot] How to support ATF on u-boot

[Kever Yang <kever.yang@rock-chips.com>]

Hi U-boot Maintainers,

     I want to upstream a new SoC named RK3399 from Rockchip which is
AARCH64/ARMv8, we need to support Arm Trust Firmware base on U-boot.

     Right now we are using a miniloader(just like SPL in U-boot) to 
load ATF/U-boot,
and PC jump from miniloader to ATF and then to U-boot(with CPU change to 
EL2 mode or nsEL1),
then U-boot load kernel/rootfs as usual.

     The ATF support for RK3399 has already upstream
     Could you give your opinion on how to support ATF on U-boot upstream?
When I asked Simon Glass offline, he suggest if we can build ATF as part 
of the
U-boot build process, perhaps with a script in U-boot tree,

Perhaps something like:

make rk3399_board_defconfig
make
./scripts/build-atf-image rk3399_board
^^ new script

In any case, a good README would help.


Thanks,
- Kever