Highmem issues with MMC filesystem

[Russell King - ARM Linux]

On Fri, Mar 19, 2010 at 02:52:00PM +0000, Catalin Marinas wrote:
> > On Fri, Mar 19, 2010 at 02:41:17PM +0000, Catalin Marinas wrote:
> > > On Thu, 2010-03-18 at 13:20 +0000, Nicolas Pitre wrote:
> > > > The only way a highmem page can be unmapped is through kunmap_atomic()
> > > > where an explicit __cpuc_flush_dcache_area() is performed, or through
> > > > flush_all_zero_pkmaps() where flush_cache_kmaps() translates into
> > > > flush_cache_all().
> > >
> > > The thing that I couldn't fully understand with the kunmap_atomic()
> > > function is that there is a path (when kvaddr < FIXADDR_START) where no
> > > cache flushing occurs. Can this not happen?
> > 
> > kunmap interfaces are not for cache flushing; the cache flushing is
> > only there to ensure consistency when unmapping a mapping on VIVT CPUs.
> 
> I agree, but then why don't we conditionally call
> __cpuc_flush_dcache_area() in kunmap_atomic() so that we avoid this
> flush on non-aliasing VIPT?

Probably because highmem was written at the time for VIVT CPUs.  I'm sure
Nicolas will accept patches to improve performance of highmem for VIPT.