Hi Roger: >-----Original Message----- >From: Roger Quadros [mailto:rogerq@xxxxxx] >Sent: Thursday, August 16, 2018 3:17 PM >To: Zengtao (B) <prime.zeng@xxxxxxxxxxxxx>; Alan Stern ><stern@xxxxxxxxxxxxxxxxxxx> >Cc: 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 16/08/18 09:21, Zengtao (B) wrote: >> 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? > >I think we should retain them as some host controllers can have issues and >these parameters give some control to system integrators to workaround if >required. > >I'm aware of one errata [1] that requires the old_scheme_first to be set in >certain circumstances. > >[1] http://www.ti.com/lit/er/sprz429l/sprz429l.pdf >Section i897 I 'd rather to use a quirk to workaround. And the main idea is to keep the enumeration flow as simple as possible. > >-- >Texas Instruments Finland Oy, Porkkalankatu 22, 00180 Helsinki. >Y-tunnus/Business ID: 0615521-4. Kotipaikka/Domicile: Helsinki
