Board specific environments and broken configs

[Sascha Hauer]

On Mon, May 17, 2021 at 01:57:56PM -0700, Trent Piepho wrote:
> On Mon, May 17, 2021 at 12:38 AM Sascha Hauer <sha at pengutronix.de> wrote:
> > On Fri, May 14, 2021 at 11:46:38PM -0700, Trent Piepho wrote:
> > >
> > > An issue with CONFIG_DEFAULT_ENVIRONMENT_PATH is that it applies to
> > > all boards in a config.  If multiple boards are built at once, e.g.
> > > imx_v7_defconfig, then there is no way for each board to have a
> > > different extra env this way.
> >
> > Thanks for spotting this. It shows some points that could be cleaned up.
> > Generally I suggest to remove the unused files. When they are unused
> > nobody should miss them. For some boards we could think about removing
> 
> Maybe the documentation could be improved, as it appears to say that a
> board env dir will automatically included?  I wonder if some boards,
> e.g. skov, thought this too and didnt' realize their env was unused.

Which part of the documentation are you referring to?

> 
> > them as well, like for example the i.MX boards that are still not
> > converted to multiimage support.
> 
> If I understand correctly, with multimage support one puts the env
> directory in the board makefile and then board code will add it.
> Doesn't this mean that every env for a supported board will be in barebox?

Yes, indeed.
Not the whole environment though, only the files that are overwritten in
the board specific environment. The remaining files are still only
present once in the binary. This scales well for the few little text
files we have, but of course isn't very size efficient once you have
bigger files like splash screens in the environment.

> 
> I was thinking there might be a way to avoid that and also avoid board
> specific code.
> 
> Pass an env overlay, or overlays, in the u-boot dtb that the pbl
> provides.  Do it like a FIT image... e.g:
> bbenv at 0 {
>     compatible = "barebox,environment-data";
>     barebox-bbenv-data = (raw data of the .bbenv goes here);
> };
> 
> The raw data is injected during build the same way a FIT image puts in
> the data for a kernel, dtb, initramfs, etc. into the FIT.
> 
> This way the env is only in the board specific image with the board
> specific barebox dtb.  And common code for barebox's dtb handler can
> trigger on the node and add it to the dtb instead of duplicating that
> in the board code.  One could also pass additional env to a chained
> barebox, though I don't know what one would do with that exactly.

That sounds doable. We wouldn't even need an overlay, just a way to
compile an environment raw image into a dtb. This might be tricky to
implement though as we would need a dependency from the dtbs into the
environment.

Sascha

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