[PATCH 0/2] arm64: configs: Provide slimmed down configuration for guests

[Mark Brown]

On Fri, Feb 10, 2023 at 02:51:23PM +0000, Mark Brown wrote:
> On Fri, Feb 10, 2023 at 02:34:03PM +0100, Arnd Bergmann wrote:

> > I wonder if we could get to a similar result by having 'defconfig'
> > still contain all platform support, but then use a fragment to
> > turn off most of the CONFIG_ARCH_* symbols which in theory
> > should also disable any platform specific drivers, provided
> > they have the usual 'depends on ARCH* || COMPILE_TEST' guard.

> That does knock out quite a lot of stuff (about 2400 options), but
> there's still a bunch of widely deployed architecture neutral stuff -
> it's about 25% of the build time of defconfig for me, whereas the
> virtconfig in these patches is about 50% of the build time.  It's a 
> combination of widely used IPs, subsystems that can't be used in
> mach-virt and off SoC devices.  We can obviously build on that approach
> though, and 25% of a big number is still a win.

Ah, now I try it properly I remember the problem with this approach: the
tooling doesn't like turning off configuration options that were
explicitly set by the base configuration:

| Value of CONFIG_ARCH_ZYNQMP is redefined by fragment ./arch/arm64/configs/virt.config:
| Previous value: CONFIG_ARCH_ZYNQMP=y
| New value: # CONFIG_ARCH_ZYNQMP is not set

It produces the expected result but does so rather loudly.  It looks
like those warnings have just been there from the start and not thought
about too hard so we should be able to fix the tool though.
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