[PATCHv2 for soc 3/4] arm: Add v7_invalidate_l1 to cache-v7.S

[Russell King - ARM Linux]

On Fri, Feb 01, 2013 at 02:10:52PM +0000, Lorenzo Pieralisi wrote:
> On Fri, Feb 01, 2013 at 12:54:17PM +0000, Russell King - ARM Linux wrote:
> > On Fri, Feb 01, 2013 at 12:11:38PM +0000, Lorenzo Pieralisi wrote:
> > > Well, on latest processors (A15, A7) caches are invalidated on reset unless
> > > the chip is programmed to skip that on reset (ie L2 retained).
> > > 
> > > But it makes sense, for sure it should not be called v7_invalidate_l1,
> > > but invalidate_louis, and instead of forcing level 0 we should be
> > > reading LoUIS and invalidate up to that level as we do in the clean and
> > > invalidate function.
> > 
> > No.  Think about it.  c7, c6, 2 _invalidates_ the cache.  That means any
> > data contained within the cache is discarded.  Data is not written back.
> > 
> > If you do this down to the LoUIS, that includes all cache levels in the
> > inner sharable domain.  The inner sharable domain includes the other CPUs
> > in the system which may already be running (certainly the boot CPU will
> > be running).
> 
> On all v7 ARM systems I know of LoUIS correspond to L1 and using LoUIS is a
> plaster that works for current systems (where by LoUIS I mean all cache
> levels down to but not inclusive of, LoUIS).

All that I'm saying is that suggesting that v7_invalidate_l1 should go
down to LoUIS is wrong, in much the same way as _invalidating_ only the
first level of cache.

However, invalidating the first level of cache only is safer than
invalidating down to LoUIS.

The only path which needs this is the secondary CPU bringup path; that's
the only path we have where some platforms give us a CPU which has only
just come out of reset, and so the caches for that CPU may be in an
unknown state.  And it only happens to a small subset of platforms.

Currently, that small subset of platforms only need the first level of
cache invalidating.  (Most platforms don't need this; most platforms
this would be a waste of time - and people seem to care about hotplug
times.)

So, that's what we should do.  And v7_invalidate_l1 is a perfectly
reasonable name for a function to do that for the V7 architecture.

As has been pointed out, there's several duplications of that.  That's
fine, let's move them into the v7 cache code.  But... let's not change
how they work and go through a pointless design exercise for
invalidating more levels of cache when we know that no platform needs
it.

If/when we do end up with a platform which requires it, we can deal
with it then.  But let's not lead people down the route of thinking
that LoUIS is suitable here when it isn't.