How to modify defconfig file - make savedefconfig?

[Alexander Dahl]

Hello Grant,

Am Thu, Jan 27, 2022 at 04:46:48PM -0000 schrieb Grant Edwards:
> What is the "right" way to modify a defconfig file?
> 
> Most sources I've found just say things like "edit the defconfig
> file". That seems error-prone -- especially when dealing with settings
> that have side effects.
> 
> I did stumble across one mention of "make savedefconfig", and this
> seems to be the right way to modify a defconfig file:
> 
>     make myboard_defconfig
>     make menuconfig
>     make savedefconfig
>     cp defconfig configs/myboard_defconfig

That's what I do.

> Do people manually edit their defconfig file when they want to make a
> change, or do they use "make savedefconfig" like I show above?

You can do both.  If you already have a defconfig, this:

1) edit your myboard_defconfig
2) make myboard_defconfig
3) make savedefconfig
4) cp defconfig configs/myboard_defconfig

You might want to `git add configs/myboard_defconfig` in between those
stages if you want to inspect what changed with those calls.

> One reason I'm asking is that the original defconfig file provided by
> the silicon vendor (Renesas) appears to be a manually stripped-down
> ..config file, because when I do
> 
>    make vendors_defconfig
>    make savedefconfig
> 
> The defconfig file generated by 'make savedefconfig' looks _nothing_
> like the starting vendors_defconfig. The new defconfig generates the
> same .config file as the vendors_defconfig file. But the
> vendors_defconfig file is arranged completely differently with
> different/extra comments, extra blank lines, etc.

I think U-Boot expects those files to be created by savedefconfig, 
see all the changesets in Git reading 
'configs: Resync with savedefconfig'.

Greets
Alex