[PATCH] powerpc/8xx: fix regression introduced by cache coherency rewrite

[Joakim Tjernlund]

Benjamin Herrenschmidt <benh at kernel.crashing.org> wrote on 28/09/2009 05:21:00:
>
> On Sun, 2009-09-27 at 15:22 +0200, Joakim Tjernlund wrote:
> > > However, adding tlbil_va() to ptep_set_access_flags() as you suggested
> > > makes everything happy. I need to test it some more, but it looks good
> > > so far. Below is what I am testing now.
> >
> > 8xx, is getting very hacky and I suspect that the only long term fix is
> > add code to trap the cache instructions in TLB error/miss and fixup the
> > exception in page fault handler. This will also have the added benefit on being able
> > to use the cache instructions in both kernel and user space like any other
> > ppc arch.
>
> First I'd like to understand exactly what's happening today, since
> it makes little sense :-) I suppose I'll have to get myself some
> 8xx doco and understand how the bloody MMU works.

hmm, I recall that the reason for the currect "force a TLB error"
procedure was to fix a problem Montavista had, possibly Tom Rini.
He fixed the problem differently at first but later it
was changed to what is in use today.

If you have access to the old linuxppc-embedded you will find a lot
of info in a thread with subject "[PATCH 2.6.14] mm: 8xx MM fix for"
Also I made a ref that I cannot access anymore:
http://ozlabs.org/pipermail/linuxppc-embedded/2005-January/016382.html

>
> Then, I saw your old patch and it's -very- invasive. If we can get away
> with a one liner just adding tlbil_va in the right place, I think I'm

Yes, my patch is invasive but that is because I did it in asm. If you do
it in the page fault handler, it will be much easier.
In principle you would only have to tag DAR and test for
the tag value in asm then branch to the page fault handler. Once there
it is easy to decode the insns.

> happy to stick with it until somebody comes up with a real good reason
> to do more :-) 8xx is on life support and has been around for long

yeah, I figured that too but Freescale seems to be cranking out new variants
still.