[U-Boot] [PATCH v3 5/7] kconfig: switch to single .config configuration

Masahiro Yamada
2015-02-24T07:20:49Z

Hi Scott,

On Mon, 23 Feb 2015 19:22:51 -0600
Scott Wood <scottwood@freescale.com> wrote:

> On Fri, 2015-02-20 at 14:24 +0900, Masahiro Yamada wrote:
> > When Kconfig for U-boot was examined, one of the biggest issues was
> > how to support multiple images (Normal, SPL, TPL). There were
> > actually two options, "single .config" and "multiple .config".
> > After some discussions and thought experiments, I chose the latter,
> > i.e. to create ".config", "spl/.config", "tpl/.config" for Normal,
> > SPL, TPL, respectively.
> >
> > It is true that the "multiple .config" strategy provided us the
> > maximum flexibility and helped to avoid duplicating CONFIGs among
> > Normal, SPL, TPL, but I have noticed some fatal problems:
> >
> > [1] It is impossible to share CONFIG options across the images.
> > If you change the configuration of Main image, you often have to
> > adjust some SPL configurations correspondingly. Currently, we
> > cannot handle the dependencies between them. It means one of the
> > biggest advantages of Kconfig is lost.
>
> Sharing can happen in the defconfig with "+S:"...

Yes, it can as for "make *_defconfig".

If we modify some options in .config for example by "make menuconfig",
we also modify some in spl/.config correspondingly.

Users are responsible for configure .config and spl/.config in sync
in the sane combination.

> What sort of dependencies are people wanting? Would it be possible to
> modify kconfig to import SPL .config into the main config (or vice
> versa?) with a name prefix so that dependencies could happen, without
> sacrificing the ability to set symbols independently?

To have independent symboles coexist in a single .config,
I can only suggest to duplicate options like
CONFIG_FOO=0x100
CONFIG_SPL_FOO=0x200
CONFIG_TPL_FOO=0x300

> Or as Ian suggested, have only the main config be user-editable, but
> still let select/depends turn certain things on/off for the
> auto-generated SPL config.

I guess it is possible for boolean options,
but impossible to set hex/int options independently.

BTW, Ian's idea had been already achieved by include/config_uncmd_spl.h

> > [2] It is too painful to change both ".config" and "spl/.config".
> > Sunxi guys started to work around this problem by creating a new
> > configuration target. Commit cbdd9a9737cc (sunxi: kconfig: Add
> > %_felconfig rule to enable FEL build of sunxi platforms.) added
> > "make *_felconfig" to enable CONFIG_SPL_FEL on both images.
> > Changing the configuration of multiple images in one command is a
> > generic demand. The current implementation cannot propose any
> > good solution about this.
>
> How about defconfig fragments? Instead of having script infrastructure
> specifically for CONFIG_SPL_FEL, merge a fragment containing
> "+S:CONFIG_SPL_FEL".

Do you mean something like this?
U-boot proper : common/.config + .config
SPL : common/.config + spl/.config
TPL : common/.config + tpl/.config

> > [3] Kconfig files are getting ugly and difficult to understand.
> > Commit b724bd7d6349 (dm: Kconfig: Move CONFIG_SYS_MALLOC_F_LEN to
> > Kconfig) has sprinkled "if !SPL_BUILD" over the Kconfig files.
>
> It seems like the root cause of this sprinkling is wanting to use
> default y to avoid touching a bunch of defconfig files, but not wanting
> to do the default y at the toplevel Kconfig. Maybe better tooling for
> bulk defconfig updates would help.

Yes. If we could move the default settings into defconfig files
(and defconfig is just for that purpose), this problem would go away.
But, in the duscussion with Simon and Alexey, we understood
maintaining many defconfigs in sync is a pain.

> In any case, couldn't you do
> CONFIG_SPL_DM currently, by making DM depend on "!SPL_BUILD || SPL_DM",
> without fundamentally changing the SPL kconfig infrastructure?

As for the Driver Model options, the dependency descriptions will get ugly,
but we won't carry them so long.
In a long run, all the boards will be converted and eventually CONFIG_DM
will bocome the default.

> Why do symbols like LOCALVERSION and CC_OPTIMIZE_FOR_SIZE depend on !
> SPL_BUILD?

These two options are used by the top-level Makefile
and it is automatically propagated to spl/*.

It is harmless to define them again in spl/.config, but meaningless.

> > [4] The build system got more complicated than it should be.
> > To adjust Linux-originated Kconfig to U-Boot, the helper script
> > "scripts/multiconfig.sh" was introduced. Writing a complicated
> > text processor is a shell script sometimes caused problems.
> >
> > Now I believe the "single .config" will serve us better. With it,
> > all the problems above would go away. Instead, we will have to add
> > some CONFIG_SPL_* (and CONFIG_TPL_*) options such as CONFIG_SPL_DM,
> > but we will not have much. Anyway, this is what we do now in
> > scripts/Makefile.spl.
>
> I had been hoping that the split configs would let us get rid of many of
> the CONFIG_SPL_* options that we already have.
>
> How will TPL be handled? Are you going to duplicate all the SPL
> symbols? Or just avoid ever kconfigizing them?

Not all, but I expect some duplicated CONFIG_TPL_* such as CONFIG_TPL_TEXT_BASE.

Currently, U-Boot runs SPL, TPL, and U-Boot proper in this order, but
in hindsight, it might have been better to run
TPL, SPL, and U-Boot proper, in this order.
In 4KB memory footprint, it is impossible to include Driver Model.
It would be a really ad-hoc implementation.

In the former order, we need CONFIG_TPL_DM,
but in the latter, we can save it.

I know TPL means "Third Program Loader", but
can we perhaps swap the order
if we assume TPL is the abbreviation of "Tiny Program Loader" ?

> > - Add some entries to include/config_uncmd_spl.h and the new file
> > scripts/Makefile.uncmd_spl. Some CONFIG options that are not
> > supported on SPL must be disabled because one .config is shared
> > between SPL and U-Boot proper going forward. I know this is not
> > a beautiful solution and I think we can do better, but let's see
> > how much we will have to describe them.
>
> How is uncmd_spl better than "!SPL_BUILD"?

We can use Kconfig as it is in Linux.

Best Regards
Masahiro Yamada