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

Scott Wood
2015-02-24T01:22:51Z

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:"...

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?

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.

> [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".

> [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. 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?

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

> [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?

> - 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"?

-Scott