From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org X-Spam-Level: X-Spam-Status: No, score=-1.0 required=3.0 tests=HEADER_FROM_DIFFERENT_DOMAINS, MAILING_LIST_MULTI,SPF_PASS,URIBL_BLOCKED autolearn=ham autolearn_force=no version=3.4.0 Received: from mail.kernel.org (mail.kernel.org [198.145.29.99]) by smtp.lore.kernel.org (Postfix) with ESMTP id 19DA7C46460 for ; Tue, 14 Aug 2018 14:39:57 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id D113721738 for ; Tue, 14 Aug 2018 14:39:56 +0000 (UTC) DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org D113721738 Authentication-Results: mail.kernel.org; dmarc=none (p=none dis=none) header.from=rowland.harvard.edu Authentication-Results: mail.kernel.org; spf=none smtp.mailfrom=linux-kernel-owner@vger.kernel.org Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1732784AbeHNR1V (ORCPT ); Tue, 14 Aug 2018 13:27:21 -0400 Received: from iolanthe.rowland.org ([192.131.102.54]:40200 "HELO iolanthe.rowland.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with SMTP id S1728458AbeHNR1V (ORCPT ); Tue, 14 Aug 2018 13:27:21 -0400 Received: (qmail 3155 invoked by uid 2102); 14 Aug 2018 10:39:53 -0400 Received: from localhost (sendmail-bs@127.0.0.1) by localhost with SMTP; 14 Aug 2018 10:39:53 -0400 Date: Tue, 14 Aug 2018 10:39:53 -0400 (EDT) From: Alan Stern X-X-Sender: stern@iolanthe.rowland.org To: "Zengtao (B)" cc: Roger Quadros , "gregkh@linuxfoundation.org" , "mathias.nyman@linux.intel.com" , "drinkcat@chromium.org" , "felipe.balbi@linux.intel.com" , "drake@endlessm.com" , "mike.looijmans@topic.nl" , "joe@perches.com" , "linux-usb@vger.kernel.org" , "linux-kernel@vger.kernel.org" Subject: RE: [PATCH] usb: hub: try old enumeration scheme first for high speed devices In-Reply-To: <678F3D1BB717D949B966B68EAEB446ED0C9B12B9@dggemm526-mbx.china.huawei.com> Message-ID: MIME-Version: 1.0 Content-Type: TEXT/PLAIN; charset=US-ASCII Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Tue, 14 Aug 2018, Zengtao (B) wrote: > Hi alan: > > >-----Original Message----- > >From: linux-usb-owner@vger.kernel.org > >[mailto:linux-usb-owner@vger.kernel.org] On Behalf Of Alan Stern > >Sent: Friday, August 10, 2018 10:20 PM > >To: Roger Quadros > >Cc: Zengtao (B) ; gregkh@linuxfoundation.org; > >mathias.nyman@linux.intel.com; drinkcat@chromium.org; > >felipe.balbi@linux.intel.com; drake@endlessm.com; mike.looijmans@topic.nl; > >joe@perches.com; linux-usb@vger.kernel.org; linux-kernel@vger.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. 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. Alan Stern