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

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Date:	Fri, 20 Jul 2007 16:59:35 -0400
From:	"Mike Frysinger" <vapier.adi@...il.com>
To:	"Mathieu Desnoyers" <mathieu.desnoyers@...ymtl.ca>,
	"Bernd Schmidt" <bernds_cb1@...nline.de>
Cc:	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:
> * Mike Frysinger (vapier.adi@...il.com) wrote:
> > 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
>
> I see, thanks for the reply. Is there a particular reason for
> implementing system.h/cmpxchg() in assembly rather that in plain C then?

honestly ?  probably not :)

Bernd would probably know best (he's good like that)
-mike
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