[Buildroot] [PATCH] boot/uboot: add option to define custom dependencies

[Thomas Petazzoni <thomas.petazzoni@bootlin.com>]

Hello Heiko,

On Sat, 25 Apr 2020 02:06:29 +0200
Heiko Stuebner <heiko@sntech.de> wrote:

> From: Heiko Stuebner <heiko.stuebner@theobroma-systems.com>
> 
> A custom uboot version my depend on additional unspecified packages
> to be built before the uboot build is attempted.
> 
> One example is an additional config fragment referencing things
> from other packages, so add an option similar to the config fragments
> where these can be defined.
> 
> Signed-off-by: Heiko Stuebner <heiko.stuebner@theobroma-systems.com>

Hm, this is interesting. Out of curiosity, what is the specific
case/issue you had ?

We already have a bunch of BR2_TARGET_UBOOT_NEEDS_xyz options:

config BR2_TARGET_UBOOT_NEEDS_DTC
config BR2_TARGET_UBOOT_NEEDS_PYLIBFDT
config BR2_TARGET_UBOOT_NEEDS_PYELFTOOLS
config BR2_TARGET_UBOOT_NEEDS_OPENSSL
config BR2_TARGET_UBOOT_NEEDS_LZOP

and I just realized that we will need:

config BR2_TARGET_UBOOT_NEEDS_PYTHON3_PYLIBFDT
config BR2_TARGET_UBOOT_NEEDS_PYTHON3_PYELFTOOLS

indeed, as of U-Boot 2020.01, a number of Python scripts, including the
pylibfdt stuff, and binman, are now Python 3 only. We already have a
few build failures in the autobuilders due to this. And
http://patchwork.ozlabs.org/project/buildroot/patch/20200413171831.12079-1-vincent.stehle at laposte.net/
enables host-python3 to get around this, but I don't see how it can
work as it doesn't guarantee that host-python3 is built before U-Boot.

So perhaps we should get rid of all this craziness and have just this
BR2_TARGET_UBOOT_CUSTOM_DEPENDENCIES ?

Questions are:

 - Is this sufficiently user-friendly? It's already not necessary easy
   to know when one has to enable NEEDS_DTC, NEEDS_PYLIBFDT, etc. So if
   instead of that one has to know that host-dtc host-python host-swig,
   etc. have to be enabled.

 - How to not break too much backward compatibility. Either we do
   Config.in.legacy handling as we usually do. Or we keep them as
   hidden booleans and have compatibility logic in uboot.mk to add the
   proper dependencies.

Yann, Peter, Arnout, any opinion on this ?

Thanks,

Thomas
-- 
Thomas Petazzoni, CTO, Bootlin
Embedded Linux and Kernel engineering
https://bootlin.com