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From:   David Laight <David.Laight@ACULAB.COM>
To:     "'paulmck@linux.ibm.com'" <paulmck@linux.ibm.com>,
        Geert Uytterhoeven <geert@linux-m68k.org>
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        lkml <linux-kernel@vger.kernel.org>,
        "linux-arch@vger.kernel.org" <linux-arch@vger.kernel.org>
Subject: RE: single copy atomicity for double load/stores on 32-bit systems
Thread-Topic: single copy atomicity for double load/stores on 32-bit systems
Thread-Index: AQHVHExZF0f//oAV60q3cSBNG5qc66aO0bMg
Date:   Thu, 6 Jun 2019 16:34:52 +0000
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From: Paul E. McKenney
> Sent: 06 June 2019 10:44
...
> But m68k is !SMP-only, correct?  If so, the only issues would be
> interactions with interrupt handlers and the like, and doesn't current
> m68k hardware use exact interrupts?  Or is it still possible to interrupt
> an m68k in the middle of an instruction like it was in the bad old days?

Hardware interrupts were always on instruction boundaries, the
mid-instruction interrupts would only happen for page faults (etc).

There were SMP m68k systems (but I can't remember one).
It was important to continue from a mid-instruction trap on the
same cpu - unless you could guarantee that all the cpus had
exactly the same version of the microcode.

In any case you could probably use the 'cmp2' instruction
for an atomic 64bit write.
OTOH setting that up was such a PITA it was always easier
to disable interrupts.

	David

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