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Subject: Re: [PATCH 2/6] 8xx: get rid of _PAGE_HWWRITE dependency in MMU.
From: Benjamin Herrenschmidt <benh@kernel.crashing.org>
To: Joakim Tjernlund <joakim.tjernlund@transmode.se>
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Date: Thu, 08 Oct 2009 11:28:19 +1100
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Cc: Scott Wood <scottwood@freescale.com>,
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On Thu, 2009-10-08 at 02:19 +0200, Joakim Tjernlund wrote:
> Benjamin Herrenschmidt <benh@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).

The DSISR munging is really not necessary I believe.

> 2.4 and 2.6 have the same handling in asm.

Yeah but the C code, especially the generic part, is different.

> 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.

> It works if I trap to C for DIRTY too.
> Before thinking on porting my old board, I want 2.4 to enjoy
> the new TLB code too :)

Hehehe.

Cheers,
Ben.