[RFC PATCH 1/3] scripts: kconfig: Add config fragment support in board/../

[Tom Rini]

On Tue, Jul 18, 2023 at 07:07:58PM -0600, Simon Glass wrote:
> Hi,
> 
> On Sun, 16 Jul 2023 at 09:12, Tom Rini <trini at konsulko.com> wrote:
> >
> > On Sat, Jul 15, 2023 at 05:40:35PM -0600, Simon Glass wrote:
> > > Hi Tom,
> > >
> > > On Thu, 13 Jul 2023 at 16:54, Tom Rini <trini at konsulko.com> wrote:
> > > >
> > > > On Wed, Jul 12, 2023 at 08:00:28AM -0600, Simon Glass wrote:
> > > > > Hi Jason,
> > > > >
> > > > > On Tue, 11 Jul 2023 at 16:29, Jason Kacines <j-kacines at ti.com> wrote:
> > > > > >
> > > > > > Add support to config fragments (.config) located in the /board
> > > > > > directory. This will allow only base defconfigs to live in /configs and
> > > > >
> > > > > Does this mean defconfigs?
> > > >
> > > > This looks like it would cover defconfig files too, but the initial
> > > > motivation is config fragments.  See
> > > > https://patchwork.ozlabs.org/project/uboot/patch/20230606071850.270001-5-clamor95@gmail.com/
> > > > for another example.
> > > >
> > > > > > all fragments to live in their respective device directory in /board/..
> > > > >
> > > > > Why do we want this? The patch should have a motivation.
> > > >
> > > > I've asked a few people to look in to this because we have a lot of
> > > > cases today of N _defconfig files where we could really instead have 1
> > > > _defconfig file and N config fragment files.  But I do not want them
> > > > living in the top level configs directory as that will get even more
> > > > unmanageable.
> > >
> > > OK I see, thank you. The patch still needs this motivation though.
> >
> > So you're saying you want the message re-worded?
> 
> Yes, to explain why.

I think the message is fine as it clearly says what it does.

> Could we also get some docs in doc/build/gcc.rst or similar?

No, I don't think that makes sense yet.  And looking at that doc, we
should split that up in to compiler specifics and then a general build
doc.  Using fragments belongs in the board docs which use fragments (as
is done in the series which have boards using fragments) and as a
general "do this to make developing your board easier" that should come
later once there's more agreement and understanding of what we can and
should do with fragments, rather than meta-options in Kconfig.

> > > > What's not in this patch (and not an ask at this point) is figuring out
> > > > how buildman could handle "foo_defconfig bar.config" as the required
> > > > config target.
> > >
> > > Indeed. Also, should they appear in the boards.cfg list?
> >
> > I doubt it? I'm not sure yet how we address getting buildman to know
> > about valid additional combinations. Take the example of something like:
> > som_vendor_carrier_defconfig + som_vendor_imx7_som.config +
> > emmc_boot_instead.config + customer_production_tweaks.config
> >
> > How would you want buildman to know about that? Does it even really need
> > to, on the other hand?  And that's not I think an uncommon example, it's
> > just splitting colibri_imx7_emmc_defconfig in to how it would be used by
> > someone taking that carrier+som to production, with their own
> > touchscreen and a few other tweaks in the dtb that needs to be passed to
> > linux.  Or the mnt reform with whatever SOM/COM you happen to have for
> > it.
> 
> Well firstly we should only worry about things that are in-tree.

Well, since I'm not letting people bring in fragments until it won't
make the configs directory even more unmanageable, we have a problem.
The problem which this patch solves.  And the example I gave above is
in-tree, except for the final step of "now make this my product", which
when it's a matter of a new device tree and config, is fine for most
cases.

> The thing is, if we don't validate that the configs at least build,
> then someone could change a config (anywhere in Kconfig or in a 'base'
> defconfig) and break the build for these 'add-on' configs. Also if

I'm not worried about this at the start. If people start trying to
enable unique drivers only in fragments, we have a problem. But based on
all of the proposed uses so far, we shouldn't see unique settings there
that we need to have compile tested all the time.

> there is no record of what fragments can be built with what, it could
> get awfully confusing.

Exactly why I want these fragments to be able to live in the board
directory rather than the top level configs directory.  Honestly, this
also opens up the possibility of moving the defconfig files from
configs/ to the board directory and I think that would be really good.

> I would suggest an interface where you can query which fragments are
> available for a board, and that buildman support building them. For
> that to work, we need some sort of structure. For example the config
> fragment could have a line listing the defconfig / .config filename it
> is intended to augment.

I'm not sure how buildman will handle fragments, if at all, but that's a
secondary consideration.  Buildman isn't used by most people and in most
cases, "make" is, and that supports (and has supported for I don't know
how many years, off-hand) config fragments.

-- 
Tom
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