linux-kernel - Re: [PATCH] usb: hub: try old enumeration scheme first for high speed devices

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Date:   Fri, 10 Aug 2018 10:19:30 -0400 (EDT)
From:   Alan Stern <stern@...land.harvard.edu>
To:     Roger Quadros <rogerq@...com>
cc:     Zeng Tao <prime.zeng@...ilicon.com>, <gregkh@...uxfoundation.org>,
        <mathias.nyman@...ux.intel.com>, <drinkcat@...omium.org>,
        <felipe.balbi@...ux.intel.com>, <drake@...lessm.com>,
        <mike.looijmans@...ic.nl>, <joe@...ches.com>,
        <linux-usb@...r.kernel.org>, <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH] usb: hub: try old enumeration scheme first for high
 speed devices

On Fri, 10 Aug 2018, Roger Quadros wrote:

> Hi,
> 
> On 10/08/18 18:01, Zeng Tao wrote:
> > The new scheme is required just to support legacy low and full-speed
> > devices. For high speed devices, it will slower the enumeration speed.
> > So in this patch we try the "old" enumeration scheme first for high speed
> > devices.
> 
> How slow does it get? Is it significant?
> Do we risk breaking existing HS devices that work? I don't think we can
> be sure till we run this through testing.

Indeed.  I am extremely skeptical about a patch like this, unless
somebody can show that Windows uses the "old" scheme for high-speed 
devices.

Alan Stern