Re: [PATCH 2/6]: powerpc/cell spidernet low watermark patch.

Arnd Bergmann
2006-08-20T10:04:04Z

On Sunday 20 August 2006 08:31, Benjamin Herrenschmidt wrote:
> > 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 ?

Right, that doesn't work. It is the only bit we use in that byte though,
so maybe it can be done with a single byte write.