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

From: Zengtao (B)
Date: Thu Aug 16 2018 - 02:21:44 EST

Hi alan:

>-----Original Message-----
>From: Alan Stern [mailto:stern@xxxxxxxxxxxxxxxxxxx]
>Sent: Tuesday, August 14, 2018 10:40 PM
>To: Zengtao (B) <prime.zeng@xxxxxxxxxxxxx>
>Cc: Roger Quadros <rogerq@xxxxxx>; 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
>On Tue, 14 Aug 2018, Zengtao (B) wrote:
>> 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
>> >> > 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
>> Yes, this is what the windows has done, you can refer to
>> 1-device-enumeration-changes-in-windows-8/
>And that blog post is 5 years old!
>Okay, I think we can go ahead and make this change. However, you should
>update the patch description to mention what Microsoft did in Windows 8 and
>say that the new behavior matches theirs.
Okay, I will update it the change log in v2.

>Also, as Roger mentioned, you should update the documentation to say that the
>old_scheme_first module parameter now applies only to low- and full-speed
>devices, since high- and SuperSpeed devices always use the old scheme first.

Since we should have dedicated enumeration flow for SS, HIGH, low and full speed devices,
So I think the old_scheme_first and use_both_schemes parameters should be removed.
What do you think about it?

>Alan Stern