linux-kernel - Re: [RFC PATCH] fix problems with NETIF_F

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Message-Id: <20100228033800N.fujita.tomonori@lab.ntt.co.jp>
Date:	Sun, 28 Feb 2010 03:38:20 +0900
From:	FUJITA Tomonori <fujita.tomonori@....ntt.co.jp>
To:	hancockrwd@...il.com
Cc:	davem@...emloft.net, bzolnier@...il.com,
	linux-kernel@...r.kernel.org, netdev@...r.kernel.org,
	linux-usb@...r.kernel.org
Subject: Re: [RFC PATCH] fix problems with NETIF_F_HIGHDMA in networking 
	drivers

On Sat, 27 Feb 2010 11:59:47 -0600
Robert Hancock <hancockrwd@...il.com> wrote:

> On Sat, Feb 27, 2010 at 3:53 AM, David Miller <davem@...emloft.net> wrote:
> > From: Robert Hancock <hancockrwd@...il.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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