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Date: Thu, 25 Mar 2010 20:35:20 -0700 (PDT)
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To: fujita.tomonori@lab.ntt.co.jp
Cc: hancockrwd@gmail.com, linux-kernel@vger.kernel.org, netdev@vger.kernel.org,
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Subject: Re: [PATCH RFC] fix problems with NETIF_F_HIGHDMA in networking
 drivers v2
From: David Miller <davem@davemloft.net>
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From: FUJITA Tomonori <fujita.tomonori@lab.ntt.co.jp>
Date: Fri, 26 Mar 2010 12:33:12 +0900

> On Thu, 25 Mar 2010 19:03:37 -0600
> Robert Hancock <hancockrwd@gmail.com> wrote:
> 
>> This seems like it could be a reasonable approach. The only thing is
>> that in this code you're returning 1 if the parent device has no DMA
>> mask set. Wouldn't it make more sense to return 0 in this case? I'm
>> assuming that in that situation it's a virtual device not backed by
>> any hardware and there should be no DMA mask restriction...
> 
> I chose the safer option because I don't know enough how net_device
> structure is used. If returning zero in such case is always safe, it's
> fine by me. any example of such virtual device driver?

Like Fujita I'd rather play it safe here.

Even for virtual devices, DMA information up to the root bus
ought to be sane.