From mboxrd@z Thu Jan  1 00:00:00 1970
From: Benjamin Herrenschmidt <benh@kernel.crashing.org>
Subject: Re: [PATCH 2/6]: powerpc/cell spidernet low watermark patch.
Date: Sun, 20 Aug 2006 16:31:49 +1000
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Cc: linuxppc-dev@ozlabs.org, akpm@osdl.org,
	James K Lewis <jklewis@us.ibm.com>,
	linux-kernel@vger.kernel.org, netdev@vger.kernel.org,
	Jeff Garzik <jgarzik@pobox.com>,
	ens Osterkamp <Jens.Osterkamp@de.ibm.com>
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To: Arnd Bergmann <arnd@arndb.de>
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> card->low_watermark->next->dmac_cmd_status |= SPIDER_NET_DESCR_TXDESFLG;
> mb();
> card->low_watermark->dmac_cmd_status &= ~SPIDER_NET_DESCR_TXDESFLG;
> card->low_watermark = card->low_watermark->next;
> 
> when we queue another frame for TX.

I would have expected those to be racy vs. the hardware... what if the
hardware is updating dmac_cmd_status just as your are trying to and the
bit out of it ?

Ben