RE: [PATCH] usb: hub: try old enumeration scheme first for high speed devices

[Zengtao (B)]

Hi alan: 

>-----Original Message-----
>From: linux-usb-owner@xxxxxxxxxxxxxxx
>[mailto:linux-usb-owner@xxxxxxxxxxxxxxx] On Behalf Of Alan Stern
>Sent: Friday, August 10, 2018 10:20 PM
>To: Roger Quadros <rogerq@xxxxxx>
>Cc: Zengtao (B) <prime.zeng@xxxxxxxxxxxxx>; gregkh@xxxxxxxxxxxxxxxxxxx;
>mathias.nyman@xxxxxxxxxxxxxxx; drinkcat@xxxxxxxxxxxx;
>felipe.balbi@xxxxxxxxxxxxxxx; drake@xxxxxxxxxxxx; mike.looijmans@xxxxxxxx;
>joe@xxxxxxxxxxx; linux-usb@xxxxxxxxxxxxxxx; linux-kernel@xxxxxxxxxxxxxxx
>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.

Yes, this is what the windows has done, you can refer to 
https://blogs.msdn.microsoft.com/usbcoreblog/2013/04/11/usb-2-1-2-0-1-1-device-enumeration-changes-in-windows-8/

>
>Alan Stern