netdev - Re: [Cbe-oss-dev] [PATCH 4/10] spidernet: zero out a pointer.

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Message-Id: <1179890607.32247.896.camel@localhost.localdomain>
Date:	Wed, 23 May 2007 13:23:27 +1000
From:	Benjamin Herrenschmidt <benh@...nel.crashing.org>
To:	Linas Vepstas <linas@...tin.ibm.com>
Cc:	Michael Ellerman <michael@...erman.id.au>, netdev@...r.kernel.org,
	Jeff Garzik <jgarzik@...ox.com>, cbe-oss-dev@...abs.org
Subject: Re: [Cbe-oss-dev] [PATCH 4/10] spidernet: zero out a pointer.


> Here's a delusional reply: I didn't see any point to it. 
> 1) a wmb would add overhead
> 2) the hardware is supposed to be looking at the status flag,
>    anyway, and not misbehaving.
> 3) there is a wmb when the descr is actually refilled in such
>    a way as to actually mean something to the hardware.
> 
> All that I really acomplished here is a minor trick to 
> aid in debug printing when looking for something bad.

And the whole thing is moot because 0 is actually a perfectly valid DMA
address :-) I suspect spider will end up trying to hit some internal
register or it's PCIe or whatever it has mapped at 0 internally and will
blow up ... At least on spider, it's not RAM there....

Ben.


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