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SubjectRe: setup.S: A20 enable sequence (once again)
Date
Followup to:  <00110620483000.11673@rob>
By author: Robert Kaiser <rob@sysgo.de>
In newsgroup: linux.dev.kernel
>
> > This doesn't really work. Neither the fast A20 gate nor the KBC is
> > guaranteed to have immediate effect (on most systems they won't.)
>
> In that case, maybe I should do repeated calls to a20_check with a
> (not too big) retry count after the port 92 write ?
>
> Problem is, it happens to work this way on all hardware I have access to,
> so I can't really reproduce such timing problems. Anyone ?
>
> > What's worse, once you have done an "out" to the KBC you need to
> > finish the sequence. I need to think about this for a bit.
>
> ??? I'm not touching the KBC if the port 92 access was successful at
> enableing A20. If, however, A20 is still disabled, I'm doing the same KBC
> sequence as the original code, so there shouldn't be any incomplete KBC
> interactions (unless I mistyped something...).
>

The problem is that your test for A20 is faulty. Severely so.
Anyway, I just sent you a patch which will terminate the first empty_8042
loop (while it's still safe) if it finds A20 now enabled.

-hpa
--
<hpa@transmeta.com> at work, <hpa@zytor.com> in private!
"Unix gives you enough rope to shoot yourself in the foot."
http://www.zytor.com/~hpa/puzzle.txt
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