[U-Boot] [PATCH 2/4] malloc_f: fix broken .config caused by CONFIG_SYS_MALLOC_F

[Simon Glass]

Hi Masahiro,

On 19 February 2015 at 00:47, Masahiro Yamada <yamada.m at jp.panasonic.com> wrote:
> Since commit b724bd7d6349 (dm: Kconfig: Move CONFIG_SYS_MALLOC_F_LEN
> to Kconfig), the ".config" created by the configuration has been
> wrong.
>
> For example, the following is a snippet of the ".config" generated
> by "make beaver_defconfig":
>
>   --------------->8-----------------
>   CONFIG_CC_OPTIMIZE_FOR_SIZE=y
>   # CONFIG_SYS_MALLOC_F is not set
>   CONFIG_SYS_MALLOC_F_LEN=0x1800
>   # CONFIG_EXPERT is not set
>   ---------------8<-----------------
>
> CONFIG_SYS_MALLOC_F_LEN is supposed to depend on CONFIG_SYS_MALLOC_F
> (see the top level Kconfig), but the ".config" above is not actually
> following that dependency.
>
> This is caused by two mistakes of commit b724bd7d6349.
>
> [1] Wrong default value of CONFIG_SYS_MALLOC_F
>   CONFIG_SYS_MALLOC_F is a boolean option, but its default value is
>   set to 0x400.

I sent a patch for this.

>
> [2] Missing "if SYS_MALLOC_F" in the default setting in each Kconfig
>   For example, arch/arm/cpu/armv7/tegra-common/Kconfig has the line
>   "default 0x1800" for SYS_MALLOC_F_LEN.  It must be described as
>   "default 0x1800 if SYS_MALLOC_F" to follow the dependency.

Does this actually matter? What does it break?

>
> Those two bugs together create such a broken ".config".
>
> Unfortunately, even if we correct both [1] and [2], the value of
> CONFIG_SYS_MALLOC_F_LEN is not set as we expect.
> The "default 0x1800 if SYS_MALLOC_F" would be simply ignored because
> the "default 0x400" in the top level Kconfig is parsed first.
>
> Notice that if multiple default lines appear for the same CONFIG,
> the first one takes precedence.

I sent a patch for this also as I don't really think the current
ordering is useful.

>
> So, this commit correct [1] and [2], also leaves some comments
> in arch/arm/cpu/armv7/tegra-common/Kconfig and arch/x86/Kconfig
> to notify not-working default values.
>
> If you want to change the default value of CONFIG_SYS_MALLOC_F_LEN,
> the easiest way would be to specify it in each *_defconfig.
>
> It is true that describing SoC-common default values in each Kconfig
> seems handy, but it often introduces nasty problems.
> If you do not understand well how Kconfig works, as you see above,
> you could easily create a broken .config file.

It is actually quite painful to not support this. If you add a new
board you need to work out what the settings should be for that board.
As we add more and more settings this is going to get even harder. It
seems much better for Tegra (for example) to be able to specify
sensible defaults that will work on most boards.

Otherwise we have no place to record that (for example) Tegra124 needs
this feature on, or this value set. Before Kconfig we have
tegra-common.h and tegra124-common.h. We discussed this problem before
and I thought it was agreed that defaults in Kconfig were the best way
forward.

If we can't use Kconfig then I think we will need to figure out
something else - perhaps includes in the defconfig files as previously
discussed. But that would be a new kconfig feature so I don't think
anyone is thrilled with the idea.

>
> The default value 0x400 is redundant for OMAP, Exynos, UniPhier, etc.
> They can be simply removed.
>
> There are still redundant "CONFIG_SYS_MALLOC_F_LEN=0x400" in many
> defconfig files, but this commit is not touching them.
>
> Signed-off-by: Masahiro Yamada <yamada.m at jp.panasonic.com>
> ---
>
[snip]

Regards,
Simon