The way to use Kconfig in U-Boot

[Bin Meng]

Hi Simon,

On Fri, May 22, 2020 at 9:38 PM Simon Glass <sjg at chromium.org> wrote:
>
> Hi,
>
> On Fri, 22 May 2020 at 06:32, Tom Rini <trini at konsulko.com> wrote:
> >
> > On Fri, May 22, 2020 at 06:20:39PM +0800, Bin Meng wrote:
> > > Hi,
> > >
> > > Kconfig is a flexible language and there are different ways to set a
> > > value for a specific platform.
> > >
> > > We can either:
> > >
> > > - Use Kconfig overriding functionality
> > > - Use Kconfig conditional set syntax like "default xxx if FOO"
> > >
> > > Based on current Kconfig files hierarchy, in the root directory we
> > > have the following come at the very beginning:
> > >
> > > # Allow defaults in arch-specific code to override any given here
> > > source "arch/Kconfig"
> > >
> > > Based on this I thought our original design was to use the overriding.
> > >
> > > But it seems not everyone is consistent on doing such. For example, we
> > > have a bunch of unmaintainable (IMO) Kconfig options like this:
> > >
> > > config SYS_MMCSD_RAW_MODE_U_BOOT_SECTOR
> > > hex "Address on the MMC to load U-Boot from"
> > > depends on SYS_MMCSD_RAW_MODE_U_BOOT_USE_SECTOR
> > > default 0x50 if ARCH_SUNXI
> > > default 0x75 if ARCH_DAVINCI
> > > default 0x8a if ARCH_MX6 || ARCH_MX7
> > > default 0x100 if ARCH_UNIPHIER
> > > default 0x140 if ARCH_MVEBU
> > > default 0x200 if ARCH_SOCFPGA || ARCH_AT91
> > > default 0x300 if ARCH_ZYNQ || ARCH_KEYSTONE || OMAP34XX || OMAP44XX || \
> > >          OMAP54XX || AM33XX || AM43XX || ARCH_K3
> > > default 0x4000 if ARCH_ROCKCHIP
> > > help
> > >   Address on the MMC to load U-Boot from, when the MMC is being used
> > >   in raw mode. Units: MMC sectors (1 sector = 512 bytes).
> > >
> > > The "default xxx if FOO" list is crazy!
> > >
> > > I think we need to discuss and come up with a unified way of doing this.
> > >
> > > I personally am in favor of the overriding mechanism, which is how
> > > current x86 architecture Kconfig is organized. In the x86 arch
> > > Kconfig, we have:
> > >
> > > # board-specific options below
> > > source "board/advantech/Kconfig"
> > > ...
> > >
> > > # platform-specific options below
> > > source "arch/x86/cpu/apollolake/Kconfig"
> > > ...
> > >
> > > # architecture-specific options below
> > >
> > > So that board behavior overrides platform/SoC behavior over
> > > architecture behavior, and over the U-Boot common Kconfig options.
> > > This to me is very clear.
> >
> > The problem I believe with overrides is that causes such churn to the
> > defconfigs on re-sync as they're used.
> >
> > Personally I think this shows one of the problems with Kconfig as a
> > language and the need for some tool to take these values from something
> > else and spit out defines.  Perhaps now that u-boot, is a defined DT
> > prefix we could something-something our way through storing these in
> > -u-boot.dtsi files and use dtoc to get a header we use everywhere ala
> > kconfig.h?
>
> I think for the case Bin mentions yes we could do that. Certainly not
> nice to put this sort of thing in Kconfig. Perhaps a DT 'config/' node
> a bit like the existing 'chosen', that dtoc emits?
>

Yes, for the example I gave, we can certainly put such information
into DT config/ node. But this example may not be a good one because
we cannot just put every Kconfig option into DT.

Regards,
Bin