RE: dcbz works on 862 everywhere!

quoted

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?

hmm, can it be that when you return from the DTLB Miss, you sometimes get an DTLB error
immediately and that DTLB Error "inherits" the DAR from the DTLB Miss?

I removed the "copy DAR to MD_EPN" part in the DTLB Error handler and my systems
runs fine.

   Jocke


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