RFC: Support for U-Boot phases in Kconfig

[Grant Likely]

On Mon, Aug 9, 2021 at 8:11 PM Tom Rini <trini at konsulko.com> wrote:
>
> On Sat, Aug 07, 2021 at 04:23:36PM -0600, Simon Glass wrote:
> > Comments welcome!
>
> I think what this is really showing is that Yamada-san was right.  All
> the games we need to do so that "make fooboard_config all" results in
> building the N stages needed was the wrong track.  Taking
> khadas-edge-v-rk3399 as an example, if we had instead of
> khadas-edge-v-rk3399_defconfig but khadas-edge-v-rk3399_tpl_defconfig
> khadas-edge-v-rk3399_spl_defconfig and khadas-edge-v-rk3399_config, each
> of which could set CONFIG_TPL, CONFIG_SPL or neither.  Then yes, to
> build u-boot-rockchip.bin you would need to pass in the separately build
> TPL and SPL stages.  But, that's true of so so many other platforms.  To
> pick another example, imx8mm_evk doesn't function without other
> binaries.  If in theory to build khadas-edge-v-rk3399 you had to do
> something like:
> $ export CROSS_COMPILE=aarch64-linux-
> $ make O=obj/tpl khadas-edge-v-rk3399_tpl_config all
> $ make O=obj/spl khadas-edge-v-rk3399_spl_config all
> $ make O=obj/khadas-edge-v-rk3399 TPL=obj/tpl/u-boot.bin \
>     SPL=obj/spl/u-boot.bin khadas-edge-v-rk3399_config all
>
> But it also meant that we didn't need to duplicate so so many Kconfig
> options and most of our obj rules would just be:
> obj-$(CONFIG_FOO) += foo.o
>
> would be a win.

Oh! I quite like this. Simpler indeed. With all the different
components that need to be pulled in to build a bootable image, each
of the various U-Boot stages would just be another configuration that
needs to be built and included in the result.

I've already been playing with a top level build tool that starts with
the U-Boot config and chooses the correct configuration of TFA, OPTEE,
and any other binaries needed. Basically it is a top level Makefile
that includes the U-Boot config and then passes make targets through
to the right build directories. This could effectively be the same
thing; start with the board config, and then filter it when going into
each stages build directory with O= as you have above.

If you want to look I've got the repo published here:

https://gitlab.arm.com/systemready/u-boot-tfa-build/

g.