[meta-xilinx] SPL->ATF->Linux

[Jean-Francois Dagenais]

Thanks Michal!

This is awesome. I can certainly use this. Please review my assumptions below...

> On Jun 12, 2019, at 07:39, Michal Simek <michal.simek at xilinx.com> wrote:
> 
> Create bif like this.
> Image - one partition load addr 0x80000 as data
> dtb - one partition load addr 0x100000000 as data
> 
> ATF - one partition (as today) EL3
> Trampoline code below() EL2-ns with filled kernel start to 0x80000 and
> dtb at 0x100000000
> 
> fsbl starts ATF and it will pass handoff structure and primary program
> will be trampoline executed in EL2 which will just pass proper arguments
> to kernel.


So in essence, the program below becomes a standalone binary file which
essentially replaces "u-boot.bin" correct? Let's call it linux-boot.bin
(inspired by comment in code below).

This would mean that boot.bin file must contain linux-boot.bin so FSBL loads it
to RAM prior to passing execution to ATF. If correct, linux-boot.bin must be
loaded at 0xfffc8000 (if following the example below), correct?

If I understand all this correctly, I could either use FSBL with a boot.bin
containing basically everything needed to boot up to the kernel, including
linux-boot.bin. Or I could use SPL inside an u-boot's mkimage made boot.bin
configured to load a FIT image containing atf, linux-boot.bin,kernelImage,dtb ?

If I understand FIT correctly, it is basically a "better", more straight forward
way to load multiples binaries into RAM rather than messing with
CONFIG_SPL_FS_LOAD_ARGS_NAME, CONFIG_SYS_SPL_ARGS_ADDR,
CONFIG_SPL_FS_LOAD_KERNEL_NAME and CONFIG_SPL_FS_LOAD_PAYLOAD_NAME... correct?

> 
> And that should be it.
> 
> /*
> * (C) Copyright 2015 - 2019, Xilinx, Inc
> *
> * Drops EL from 3 down to 2 and sets up the CPU for AArch64 execution.
> *
> * The kernel start address and DTB location can easily be patched at
> runtime
> * before jumping to this code-snippet if needed.
> *
> * To for example build and link to 0xfffc8000:
> * aarch64-none-elf-gcc -nostartfiles -nodefaultlibs \
> *                      -Wl,--build-id=none,-Ttext=0xfffc8000
> linux-boot.s -o linux-boot
> *
> * Written by Edgar E. Iglesias and Jason Wu.
> */
>        .section        .text
>        .global         _start
> _start:
>        ldr     x17, kernel_start
>        ldr     x0, kernel_dts
>        mov     x1, xzr
>        mov     x2, xzr
>        mov     x3, xzr
>        blr     x17
>        .balign 8
> kernel_start:
>        .dword  ${kernel_start}
> kernel_dts:
>        .dword  ${kernel_dts}

Thanks again for taking the time. I shall submit a patch in README.booting.md if
my endeavour looks upstreamable.