Re: [Qemu-devel] [RFC PATCH 1/5] ppc64: Express dependencies of 'pseries' and 'powernv' machines with kconfig

[Paolo Bonzini]

On 30/01/19 10:43, Thomas Huth wrote:
> CONFIG_SPAPR_RNG should stay in the ppc-softmmu.mak file since this
> is a completely optional device.

What about making it

    default y

and adding to the .mak file this:

#CONFIG_SPAPR_RNG=n

I think the two approaches are more or less equivalent, but
"#CONFIG_FOO=n" has a small advantage when the feature has a build-time
dependency, such as CONFIG_MILKYMIST_TMU2's dependency on OpenGL.  In
that case,

   CONFIG_MILKYMIST_TMU2=y

would report a contradiction if OpenGL is not available at build time, while

   default y
   ...
   #CONFIG_MILKYMIST_TMU2=n

would not.

In any case, there are many many such cases in x86 (QXL, HYPERV, FDC,
SEV, ISA_IPMI_*, APPLESMC, SGA, HPET, VTD, AMD_IOMMU, PVPANIC, TPM_TIS,
TPM_CRB) and they should be handled in the same way---and especially
they should be mentioned in the default-configs/ file under "Optional
devices".  So thanks for noticing this case!

Paolo