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From: David Miller <davem@davemloft.net>
Subject: Re: [RFC/T] [NET] make pskb_expand_head warn when called with
 invalid state
Date: Tue, 13 May 2008 01:38:02 -0700 (PDT)
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From: Johannes Berg <johannes@sipsolutions.net>
Date: Tue, 13 May 2008 10:32:08 +0200

> > FWIW, the only practical case where this can occur is for an SG+CSUM
> > device which cannot handle DMA'ing highmem pages, and we get such a
> > page via sendfile() or similar.
> 
> That's well possible since I'm using sungem and it says "no highdma" but
> "sg/hwcsum" for my hardware, and I do have highmem.

It appears only some sungem parts support full 64-bit DMA, so
yes that's indeed possible.