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Date: Tue, 13 Dec 2016 08:24:08 -0500 (EST)
From: Alan Stern <stern@rowland.harvard.edu>
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To: John Stultz <john.stultz@linaro.org>
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        Wei Xu <xuwei5@hisilicon.com>, Guodong Xu <guodong.xu@linaro.org>,
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Subject: Re: [RFC][PATCH 5/5] usb: dwc2: Add a quirk to allow speed negotiation
 for Hisilicon Hi6220
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On Mon, 12 Dec 2016, John Stultz wrote:

> From: Chen Yu <chenyu56@huawei.com>
> 
> The Hi6220's usb controller is limited in that it does not
> support "Split Transactions", so it does not support communicating
> with low-speed and full-speed devices behind a high-speed hub.
> 
> Thus it requires a quirk so that we can manually drop the usb
> speed when low/full-speed are attached, and bump back to high
> speed when they are removed.

Just out of curiosity (I know nothing about this hardware), what 
happens if there is a high-speed hub plugged into the host controller 
and both a high-speed and a full-speed device plugged into the hub?  

Do you end up forcing the high-speed device to run at full speed?

Alan Stern