Re: [RFC PATCH 00/23] arm: defconfigs: use kconfig fragments

[Arnd Bergmann]

On Wednesday, December 7, 2016 12:41:29 PM CET Bartlomiej Zolnierkiewicz wrote:
> 
> On Tuesday, December 06, 2016 11:03:34 AM Olof Johansson wrote:
> > On Tue, Dec 6, 2016 at 4:38 AM, Bartlomiej Zolnierkiewicz
> > <b.zolnierkie@xxxxxxxxxxx> wrote:
> > > Hi,
> > >
> > > This RFC patchset starts convertion of ARM defconfigs to use kconfig
> > > fragments and dynamically generate defconfigs.  The goals of this
> > > work are to:
> > 
> > You don't provide any motivation as to why this is better. As far as I
> 
> Benefits are:
> 
> - no code duplication (this initial patchset alone removes ~1700 lines
>   from defconfigs without any change in functionality)

This may be interesting

> - prevention of "multi" defconfigs (i.e. multi_v7_defconfig) going out
>   of sync with "SoC-family" ones (i.e. exynos_defconfig) - there will
>   be just one place to update when changing things

I'm not convinced this is worthwhile: in a lot of cases, the soc-specific
configs want to enable things built-in, while the more generic ones
tend to use loadable modules.

> - possibility to add support for more optimized defconfigs (i.e. board
>   specific ones) in the future without duplicating the code

I'd prefer seeing fewer top-level options than more of them, so
this doesn't really help.

> - making it easier to define arch specific parts of defconfigs in
>   the future if we decide on doing it (i.e. we may want to enable
>   things like CONFIG_SYSVIPC for all defconfigs)

The example you give is for something that should be decided
in architecture-independent Kconfig language rather than
per architecture, and that won't require fragments.

> > am concerned it'll just be a mess.
> > 
> > So:
> > 
> > Nack. So much nack. I really don't want to see a proliferation of
> > config fragments like this.
> > 
> > I had a feeling it was a bad idea to pick up that one line config
> > fragment before, since it opened the door for this kind of mess. 
> 
> Like I said in the cover-letter I'm not satisfied with the current
> patches and they have much room for improvement.
> 
> However I see that you don't like the idea itself... 

I do think that there is some room for more config fragments in
mainline, but not most of the patches you have here. Some areas
that I think would benefit from fragments are:

- architecture level selection: v6/v6k/v7/v7ve/v8 could have a
  common defconfig file that starts out with all v6+ enabled,
  but then having fragments that disable the older architectures
  and platforms using them while turning on features that are only
  available on newer architectures

- A "debug" fragment would be nice, to turn on common options that
  add a lot of useful runtime checks at the expense of performance
  or code size.

- A "distro" fragment that turns on all loadable modules that are
  enabled by common distributions (e.g. two or more of
  debian/fedora/opensuse/gentoo), to let you build a drop-in
  replacement kernel for a shipping distro. This would also allow
  the distros to strip their own config files and just specify
  whatever differs from the others.

	Arnd