Re: Time to get rid of CPU6 ERRATA on powerpc/8xx ?

On Sun, Jan 07, 2018 at 06:51:26PM +0100, christophe leroy wrote:

Le 07/01/2018 à 17:43, Segher Boessenkool a écrit :

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On Sun, Jan 07, 2018 at 05:23:13PM +0100, christophe leroy wrote:

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Today, Linux kernel includes a workaround for CPU6 ERRATA on the 8xx
powerpc.

This ERRATA exists on the 801, the 823, the 855/860 before revision C.0
It doesn't concern any modern versions of the 8xx, neither the 860 past
and including rev C.0, nor the 866 nor the 885

This workaround complicates the TLBmiss and TLBerror handlers and make
the code more and more unreadable.

Since this workaround addresses very old versions of the 8xx, I'd like
to get rid of it. Do you see any good reason to keep it today ? If not I
will come with a cleanup patch in the coming weeks.

What is "very old"?  It'll help if you give some indication.

CPU6 bug is already announced fixed in rev C.0 in revision 1.4 of the 
ERRATA document, issued in August 2000.

And that is the newest chip that had the bug?  Wow, very old indeed then.

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Removing the workarounds is fine by me, of course...  Maybe make it fail
to boot though, with an error message?  Someone *will* try to run it on
an old system, *especially* if you think no one would.

Ok, will see how we can do that. It means identifying each revision of 
the chip.

If it is *that* old you may not have to bother...  Up to the maintainers
of course.


Segher