Date:   Mon, 27 Feb 2023 13:00:43 -0500
From:   Tom Rini <trini@konsulko.com>
To:     Masahiro Yamada <masahiroy@kernel.org>
Cc:     Simon Glass <sjg@chromium.org>,
        U-Boot Mailing List <u-boot@lists.denx.de>,
        lk <linux-kernel@vger.kernel.org>
Subject: Re: [PATCH] kconfig: Proposed language extension for multiple builds
Message-ID: <Y/zvy71oZAU5YO8w@bill-the-cat>
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On Mon, Feb 27, 2023 at 11:52:57PM +0900, Masahiro Yamada wrote:
> Hi Simon,
>=20
> On Mon, Feb 27, 2023 at 1:00=E2=80=AFPM Simon Glass <sjg@chromium.org> wr=
ote:
> >
> > Hi Masahiro,
> >
> > On Sun, 26 Feb 2023 at 20:36, Masahiro Yamada <masahiroy@kernel.org> wr=
ote:
> > >
> > > Hi Simon,
> > >
> > > On Mon, Feb 27, 2023 at 4:23=E2=80=AFAM Simon Glass <sjg@chromium.org=
> wrote:
> > > >
> > > > Hi Masahiro,
> > > >
> > > > On Sun, 26 Feb 2023 at 10:36, Masahiro Yamada <masahiroy@kernel.org=
> wrote:
> > > > >
> > > > > On Sun, Feb 26, 2023 at 11:44=E2=80=AFPM Tom Rini <trini@konsulko=
=2Ecom> wrote:
> > > > > >
> > > > > > On Sun, Feb 26, 2023 at 11:32:03PM +0900, Masahiro Yamada wrote:
> > > > > > > On Sun, Feb 26, 2023 at 11:04=E2=80=AFPM Simon Glass <sjg@chr=
omium.org> wrote:
> > > > > > > >
> > > > > > > > Hi Masahiro,
> > > > > > > >
> > > > > > > > On Sat, 25 Feb 2023 at 20:31, Masahiro Yamada <masahiroy@ke=
rnel.org> wrote:
> > > > > > > > >
> > > > > > > > > On Sat, Feb 25, 2023 at 11:38=E2=80=AFAM Simon Glass <sjg=
@chromium.org> wrote:
> > > > > > > > > >
> > > > > > > > > > +Masahiro Yamada
> > > > > > > > >
> > > > > > > > >
> > > > > > > > >
> > > > > > > > >
> > > > > > > > > I do not know.
> > > > > > > > > This seems a shorthand in Kconfig level.
> > > > > > > > >
> > > > > > > > >
> > > > > > > > > masahiro@zoe:~/ref/u-boot(master)$ rgrep '^config SPL_' |=
 wc
> > > > > > > > >     540    1080   24872
> > > > > > > > > masahiro@zoe:~/ref/u-boot(master)$ rgrep '^config TPL_' |=
 wc
> > > > > > > > >     163     326    7462
> > > > > > > > >
> > > > > > > > > If hundreds of duplications are not manageable,
> > > > > > > > > go for it, but kconfig will be out-of-sync from the
> > > > > > > > > upstream Kconfig.
> > > > > > > >
> > > > > > > > Yes that's right, it is a shorthand in Kconfig.
> > > > > > > >
> > > > > > > > The counts above understand the problem a little since quit=
e a few
> > > > > > > > CONFIG options without an SPL prefix are used in SPL. We do=
n't have
> > > > > > > > tools to estimate how many, and we sometimes add a new symb=
ol to 'gain
> > > > > > > > control' of a particular feature in a phase.
> > > > > > > >
> > > > > > > > My intent in sending this patch was to check whether this s=
upport for
> > > > > > > > configuring multiple related builds (or something like it) =
could go
> > > > > > > > upstream, which for Kconfig is Linux, I believe. What do yo=
u think?
> > > > > > >
> > > > > > >
> > > > > > > This complexity is absolutely unneeded for Linux.
> > > > > > >
> > > > > > > So, the answer is no.
> > > > > >
> > > > > > Well, I think Simon summarized himself a bit shorter here than =
he did in
> > > > > > the patch itself.  So, to what extent does the kernel want to c=
onsider
> > > > > > all of the other projects using the Kconfig language and their =
needs /
> > > > > > use cases?
> > > > > >
> > > > > > --
> > > > > > Tom
> > > > >
> > > > >
> > > > >
> > > > > In principle, only features that are useful for Linux.
> > > >
> > > > I'm disappointed in this attitude. It is the same thing that we saw
> > > > from the DT bindings until recently.
> > >
> > >
> > > Sorry, but this is the maintainer's job.
> > > Saying no is one of the most important jobs as a maintainer.
> > >
> > > I must avoid Kconfig getting Frankenstein mechanisms.
> >
> > Can you suggest a better approach?
>=20
>=20
> No, I can't.
>=20
> Kconfig is a configuration system of the Linux kernel, which is monolithi=
c.

Well, Kconfig is a configuration system used by a dozen projects, that
started out in Linux to replace the old Config.in system (which it has
done a great job of, with my old timer hat on).

> It was not designed with multi-phase images in mind.

Yes, it was designed to move from the old Config.in to something better,
that's why it still has "# FOO is not set" rather than FOO=3Dn :)

> Presumably, Kconfig is good for U-Boot proper, but not for SPL/TPL given
> the limited memory. There is little room for user's configuration anyway.
>=20
> U-Boot extended SPL too much.
> On-chip RAM is not supposed to run DT, DM, FIT.
> With SPL kept simple and ad-hoc, none of
> CONFIG_SPL_OF_CONTROL, SPL_DM, SPL_FIT was unneeded.
> "bootph-*" properties were unneeded either.

Yes, you disagree with the path U-Boot has taken in some areas. I do
find this regrettable as you were a valued contributor to the project.

The place Kconfig is a bad fit in U-Boot isn't SPL/TPL/VPL, but for
values, hex/int are used more in U-Boot than they are in the Linux
kernel, which says something, and it's something we should deal with in
U-Boot.

> This is a U-Boot-specific problem.
> Please solve it in U-Boot.

Well, I keep going back and forth on if the modules part of the Linux
kernel Kconfig and Kbuild system could be handled in a more clean, or
just different manner, or not.  And as Simon noted in the original
email, Zephyr is likely to have the same conceptual issue soon enough.
At a quick glance, barebox "PBL" could also make use of the Kconfig
construct if they wanted (something like MCI_IMX_ESDHC could have
"phases default pbl" added, instead of listing MCI_IMX_ESDHC_PBL later
on). So I disagree that this is a problem specific to U-Boot, and that's
why I've been encouraging Simon to bring this up more widely, so we can
be good community members and help the Kconfig language community at
large.

--=20
Tom

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