dcbz works on 862 everywhere!

[Joakim Tjernlund]

> Hi list
>
> I have been researching why I can't use dcbz and friends on 8xx CPU.
> Till Strauman found out long ago that the dcxx instuctions did not update
> the DAR register and that was the key I needed.
>
> After a lot of testing/reading I found a 2 instruction workaround
> that lets me use dcbz in copy_tofrom_user().
> I can also used dcbz in a user space app without problems. I even
> removed the TLB change bit hack by Tom Rini and everything works.
>
> By copying the MD_EPN register to the DAR register in the DTLB Miss handler
> just before MD_RPN is written everything just works. The only explanation that
> makes sense to me is that the MD_RPN has a undocumented dependency to the DAR
> register, the 20 msb of MD_EPN and DAR needs to be the same before MD_RPN is written.

hmm, this is not quite correct. I can copy MD_EPN to DAR after the write to MD_RPN
and it still works. Seems like DAR must be correct when rfi is executed. I wonder
why?

 Jocke


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