[PATCH V2] mm/ioremap: Probe platform for p4d huge map support

[Andrew Morton]

On Fri, 28 Jun 2019 10:50:31 +0530 Anshuman Khandual <anshuman.khandual at arm.com> wrote:

> Finishing up what the commit c2febafc67734a ("mm: convert generic code to
> 5-level paging") started out while levelling up P4D huge mapping support
> at par with PUD and PMD. A new arch call back arch_ioremap_p4d_supported()
> is being added which just maintains status quo (P4D huge map not supported)
> on x86, arm64 and powerpc.

Does this have any runtime effects?  If so, what are they and why?  If
not, what's the actual point?