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From: David Miller <davem@davemloft.net>
Subject: Re: [Uclinux-dist-devel] [PATCH 1/5] netdev: bfin_mac: Blackfin
 EMAC interrupt may not be shared
Date: Fri, 29 May 2009 15:18:16 -0700 (PDT)
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From: Mike Frysinger <vapier.adi@gmail.com>
Date: Fri, 29 May 2009 18:13:02 -0400

> the difference is that one of these is required in order for anything
> to get done and the other is always useless noise.  also, the Blackfin
> core does do speculative data fetching on external memory, but not
> MMRs, so the stalling due to the data cache line fills will be
> mitigated unlike the useless MMR reads.

You only need to read the register if the descriptor status is not
ready yet, and you're just spinning in that case anyways.

I doubt it makes any real difference if implemented properly.

But I guess it's more fun to speculate than to actually try it out.
:-/