[PATCH 2/6] 8xx: get rid of _PAGE_HWWRITE dependency in MMU.

[Joakim Tjernlund]

Benjamin Herrenschmidt <benh at kernel.crashing.org> wrote on 08/10/2009 02:28:19:
>
> On Thu, 2009-10-08 at 02:19 +0200, Joakim Tjernlund wrote:
> > Benjamin Herrenschmidt <benh at kernel.crashing.org> wrote on 08/10/2009 02:04:56:
> > >
> > >
> > > > Yes it does. If one adds HWEXEC it will fail, right?
> > >
> > > Why ? We can just filter out DSISR, we don't really care why it failed
> > > as long as we know whether it was a store or not.
> > >
> > > > Also this count as a read and you could easily end up
> > > > in the protection case(in 2.4 you do)
> > >
> > > I'm not sure what you mean by "the protection case" Again, the C code
> > > shouldn't care.
> >
> > it does, and it should. How else should you know if you try
> > to read a NA space?
>
> Generic code should sort it out in handle_mm_fault() (or earlier if it
> can't find a VMA at all).

How can it? You need to know more that just read and write.

>
> The DSISR munging is really not necessary I believe.

Well, it is today and I don't see how you can remove it.

>
> > 2.4 and 2.6 have the same handling in asm.
>
> Yeah but the C code, especially the generic part, is different.

yes, but it seem to work the same.

>
> > hmm, maybe I should just call C, but 8xx isn't a speed monster so every
> > cycle counts :)
>
> But that's a slow path anyways.

How so? You take a TLB Error for the first write to
every page.

 Jocke