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From: Segher Boessenkool <segher@kernel.crashing.org>
Subject: Re: [PATCH] qe_ic: Do a sync when masking interrupts.
Date: Mon, 23 Oct 2006 20:46:01 +0200
To: Scott Wood <scottwood@freescale.com>
Cc: Paul Mackerras <paulus@samba.org>, linuxppc-dev@ozlabs.org
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>> If a sync after an MMIO write is enough, then (in almost all
>> cases) so is an eieio.
>
> In this case, the spurious interrupts still happen with eieio, but  
> not with sync.  It's probably synchronizing the MMIO write with  
> some unrelated load from memory (such as reading the stack frame to  
> return from the mask function, or reading action->flags to  
> determine whether to check for IRQ_DISABLED).

Yes, it sure sounds like the only reason the sync insn helps
is that it causes a (small) delay.  If you document this (and
also that it isn't required for correctness) in the code, I
don't think anyone will complain / be curious about it anymore.


Segher