Date: Sun, 28 Feb 2010 03:38:20 +0900
To: hancockrwd@gmail.com
Cc: davem@davemloft.net, bzolnier@gmail.com, linux-kernel@vger.kernel.org,
       netdev@vger.kernel.org, linux-usb@vger.kernel.org
Subject: Re: [RFC PATCH] fix problems with NETIF_F_HIGHDMA in networking 
	drivers
From: FUJITA Tomonori <fujita.tomonori@lab.ntt.co.jp>
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	<20100227.015350.71138134.davem@davemloft.net>
	<51f3faa71002270959o4d1435e3xf67185fccaf50b18@mail.gmail.com>
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On Sat, 27 Feb 2010 11:59:47 -0600
Robert Hancock <hancockrwd@gmail.com> wrote:

> On Sat, Feb 27, 2010 at 3:53 AM, David Miller <davem@davemloft.net> wrote:
> > From: Robert Hancock <hancockrwd@gmail.com>
> > Date: Fri, 26 Feb 2010 21:08:04 -0600
> >
> >> That seems like a reasonable approach to me. Only question is how to
> >> implement the check for DMA_64BIT. Can we just check page_to_phys on
> >> each of the pages in the skb to see if it's > 0xffffffff ? Are there
> >> any architectures where it's more complicated than that?
> >
> > On almost every platform it's "more complicated than that".
> >
> > This is the whole issue. ?What matters is the final DMA address and
> > since we have IOMMUs and the like, it is absolutely not tenable to
> > solve this by checking physical address attributes.
> 
> Yeah, physical address isn't quite right. There is a precedent for

Probably, you need to check PCI_DMA_BUS_IS_PHYS.
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