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

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Date:   Thu, 16 Aug 2018 06:21:33 +0000
From:   "Zengtao (B)" <prime.zeng@...ilicon.com>
To:     Alan Stern <stern@...land.harvard.edu>
CC:     Roger Quadros <rogerq@...com>,
        "gregkh@...uxfoundation.org" <gregkh@...uxfoundation.org>,
        "mathias.nyman@...ux.intel.com" <mathias.nyman@...ux.intel.com>,
        "drinkcat@...omium.org" <drinkcat@...omium.org>,
        "felipe.balbi@...ux.intel.com" <felipe.balbi@...ux.intel.com>,
        "drake@...lessm.com" <drake@...lessm.com>,
        "mike.looijmans@...ic.nl" <mike.looijmans@...ic.nl>,
        "joe@...ches.com" <joe@...ches.com>,
        "linux-usb@...r.kernel.org" <linux-usb@...r.kernel.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: RE: [PATCH] usb: hub: try old enumeration scheme first for high
 speed devices

Hi alan:

>-----Original Message-----
>From: Alan Stern [mailto:stern@...land.harvard.edu]
>Sent: Tuesday, August 14, 2018 10:40 PM
>To: Zengtao (B) <prime.zeng@...ilicon.com>
>Cc: Roger Quadros <rogerq@...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 Tue, 14 Aug 2018, Zengtao (B) wrote:
>
>> Hi alan:
>>
>> >-----Original Message-----
>> >From: linux-usb-owner@...r.kernel.org
>> >[mailto:linux-usb-owner@...r.kernel.org] On Behalf Of Alan Stern
>> >Sent: Friday, August 10, 2018 10:20 PM
>> >To: Roger Quadros <rogerq@...com>
>> >Cc: Zengtao (B) <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.
>>
>> 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/
>
>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