dcbz works on 862 everywhere!

[Joakim Tjernlund]

> Joakim Tjernlund wrote:
>
> > hmm, no response from the maintainer(s). You don't agree?
>
> It's interesting to watch these hacks, but I can't justify
> complicating a general purpose function with more bus cycles by
> emulating a functional problem.  By not using these instructions
> we have a working system that costs just a few more cycles during
> the memory copy/zero operations.  If we had _working_ dcbz
> instructions, it would be a gain to use them, but from a system
> perspective it is going to cost more to "fix up" these than
> the code that already exists.

Look a little harder. I am not talking just about dcbz, dcbi has
the same problem. As it stands today, there are real bugs w.r.t dcbi.

consistent_alloc() causes DTLB errors with a incorrect address in DAR.
Just force DAR to an invalid address in the DTLB Miss handler before
you leave it and see if you kernel boots.

> As I said in the past, I'm sensitive to the code in the TLB exception
> processing.  So do something to remove code and streamline the process
> and I'm really interested.  Do something to add more code and it's
> going to get placed pretty low in my pile of things to do.

Yes I know, but you are not reading what am writing. For instance,
the change below does not add to the fast path of the DTLB Miss handler and
it fixes a real problem:
> I just want to point out(again) that TLB Miss caused by most of the
> dcxx(dcbf, dcbi, dcbst, dcbz) instructions that end up in the slow path(DataAccess)
> don't work with the current impl. since DAR isn't set. The code fragment below
> will fix that(from my earlier patch). This won't affect the fast path at all
> since it all of it can be in the slow path.
>
> +	/* Copy 20 msb from EPN to DAR since the dcxx instructions fails
> +	 * update the DAR when they cause a DTLB Miss.
> +	 */
> +	mfspr	r21, MD_EPN
> +	rlwinm	r21, r21, 0, 0, 19
> +	mfspr	r20, DAR
> +	rlwinm	r20, r20, 0, 20, 31
> +	or	r20, r20, r21
> +	mtspr	DAR, r20

Go back and think dcbi instead of dcbz.

     Jocke


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