linux-kernel - Re: blackfin - cmpxchg not atomic ?

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Date:	Fri, 20 Jul 2007 16:36:12 -0400
From:	"Mike Frysinger" <vapier.adi@...il.com>
To:	"Mathieu Desnoyers" <mathieu.desnoyers@...ymtl.ca>
Cc:	tonyko@...eo.ca, robin.getz@...log.com,
	linux-kernel@...r.kernel.org
Subject: Re: blackfin - cmpxchg not atomic ?

On 7/20/07, Mathieu Desnoyers <mathieu.desnoyers@...ymtl.ca> wrote:
> I am currently passing through each architectures adding a
> cmpxchg_local() to each system.h, and I notice that you disable
> interrupts in your cmpxchg() implementation, why are you doing so ?

because Blackfin lacks any atomic instructions

> Also, does you assembly stub _really_ modify memory atomically ? If yes,
> then there should be no need for disabling interrupts. Else, I see a
> major problem with SMP.

that isnt the only problem with SMP on Blackfin

> I also don't like the comment in asm-blackfin/atomic.h :
>
>  * Generally we do not concern about SMP BFIN systems, so we don't have
>  * to deal with that.
>
> I have seen on the blackfin website that you actually sell a board with
> SMP. Why aren't you caring about it ?

just because a processor has more than one core does not make it SMP
-mike
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