[RFC 3/4] powerpc: Add pmem API support

[Dan Williams]

On Tue, Jun 27, 2017 at 3:28 AM, Oliver O'Halloran <oohall at gmail.com> wrote:
> Adds powerpc64 implementations of:
>
>         memcpy_flushcache()
>         arch_wb_cache_pmem()
>         arch_invalidate_pmem()
>
> Which form the architecture-specific portition of the persistent memory
> API. These functions provide cache-management primitives for the DAX
> drivers and libNVDIMM.
>

Ok, now that we have commit 0aed55af8834 "x86, uaccess: introduce
copy_from_iter_flushcache for pmem / cache-bypass operations" upstream
that changes the model for how an architecture advertises
pmem-specific cache management routines. CONFIG_ARCH_HAS_PMEM_API
causes the pmem driver to try to link to these helpers rather than
dummy fallbacks:

    arch_wb_cache_pmem
    arch_invalidate_pmem

....and CONFIG_ARCH_HAS_UACCESS_FLUSHCACHE indicates that the arch has
all the needed "flushcache" apis:

    __copy_from_user_flushcache
    memcpy_page_flushcache
    memcpy_flushcache