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 >devices > >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 >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
