[U-Boot] [PATCH v2 3/4] kconfig: switch to single .config configuration

[Stephen Warren <swarren@wwwdotorg.org>]

On 02/19/2015 12:55 AM, 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.
>
> [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.
>
> [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.
>
> [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 admit my mistake with my apology and this commit switches to the
> single .config configuration.
>
> It is not so difficult to do that:
>
>   - Remove unnecessary processings from scripts/multiconfig.sh
>    This file will remain for a while to support the current defconfig
>    format.  It will be removed after more cleanups are done.
>
>   - Adjust some makefiles and Kconfigs
>
>   - 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.
>
>   - update doc/README.kconfig
>
> More cleaning up patches will follow this.

> diff --git a/arch/arm/cpu/armv7/tegra-common/Kconfig b/arch/arm/cpu/armv7/tegra-common/Kconfig
> index 0de13ae..c9e8919 100644
> --- a/arch/arm/cpu/armv7/tegra-common/Kconfig
> +++ b/arch/arm/cpu/armv7/tegra-common/Kconfig
> @@ -26,7 +26,7 @@ config SYS_MALLOC_F_LEN
>   	default 0x1800 if SYS_MALLOC_F
>
>   config USE_PRIVATE_LIBGCC
> -	default y if SPL_BUILD
> +	default y
>
>   config DM
>   	default y if !SPL_BUILD

I think the above patch demonstrates the problem very nicely; it changes 
the semantics from having CONFIG_USE_PRIVATE_LIBGCC enabled only in SPL 
build to having it enabled everywhere. While that particular change 
shouldn't be an issue, I think that requiring that all config options to 
have the same value in main/SPL/TPL will be. For example, how do we 
disabled MMC support in SPL? We have to introduce separate CONFIG_MMC 
and CONFIG_SPL_MMC don't we? That doesn't seem any better than having 
separate defconfig files for SPL/non-SPL, or using ifdefs in a single 
defconfig file. What happened to the ability of one defconfig file to 
include another, so options could be shared between the two?