linux-kernel - Re: [PATCH 2.6.34] ehci-hcd: add option to enable 64-bit DMA support

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Message-ID: <4B85EE88.5050506@kernel.org>
Date:	Thu, 25 Feb 2010 12:29:12 +0900
From:	Tejun Heo <tj@...nel.org>
To:	Yuhong Bao <yuhongbao_386@...mail.com>
CC:	hancockrwd@...il.com, david-b@...bell.net, greg@...ah.com,
	linux-kernel@...r.kernel.org, linux-usb@...r.kernel.org
Subject: Re: [PATCH 2.6.34] ehci-hcd: add option to enable 64-bit DMA support

Hello,

On 02/25/2010 12:15 PM, Yuhong Bao wrote:
>> (following thread from the ATA side) I'm with Greg on this. USB2.0 is
>> quite slow on today's standard and most 64bit machines now have IOMMU
>> of some kind anyway. 
> 
> Except that unfortunately, Intel with Lynnfield and Clarkdale decided 
> to do market segmentation on the VT-d feature. 
> This could be done because both have an integrated northbridge.
> With Lynnfield, the very common Core i5 750 CPU do not support VT-d,
> but the Core i7 800 series does.
> With Clarkdale, the very common Core i3 500 series do not support VT-d,
> but the Core i5 600 series does, except the 661.
> Not to mention that in the Core 2 generation, VT-d was available only
> on Q35/Q45/X38/X48 chipsets.

Arghhh.... I hate when intel pulls this type of 'product
differentiation' stunts.  At any rate, I'm doubtful swiotlb'ing for
usb2.0 would be noticeable at all.

Thanks.

-- 
tejun
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