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

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Date:	Thu, 25 Feb 2010 08:14:13 -0800
From:	Greg KH <greg@...ah.com>
To:	Tejun Heo <tj@...nel.org>
Cc:	Oliver Neukum <oliver@...kum.org>,
	Yuhong Bao <yuhongbao_386@...mail.com>, hancockrwd@...il.com,
	david-b@...bell.net, 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

On Thu, Feb 25, 2010 at 02:25:34PM +0900, Tejun Heo wrote:
> On 02/25/2010 01:03 PM, Oliver Neukum wrote:
> > Am Donnerstag, 25. Februar 2010 04:29:12 schrieb Tejun Heo:
> >> 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.
> > 
> > That can and should be tested.
> 
> Robert did already.  Given that USB2.0 devices aren't usually used for
> high-perf storage subsystem, the benefit looks marginal to me but
> everyone is entitled to own opinion.

For now, I'd like to not enable this, given the huge risks and no known
benifit.

For USB 3.0, we can reconsider it, as it might start to make a
difference there.

thanks,

greg k-h
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