Re: [PATCH v5] USB: core: skip unconfiguration if device doesn't support it

[Greg KH <gregkh@linuxfoundation.org>]

On Fri, May 13, 2022 at 10:26:02AM -0400, Alan Stern wrote:
> On Fri, May 13, 2022 at 04:13:07PM +0200, Greg KH wrote:
> > On Fri, May 13, 2022 at 10:09:26AM -0400, Alan Stern wrote:
> > > On Fri, May 13, 2022 at 11:50:26AM +0200, Jose Ignacio Tornos Martinez wrote:
> > > > Ok, I will try to identify the "bad" devices in some way.
> > > > 
> > > > Thanks
> > > > 
> > > > José Ignacio
> > > > 
> > > > 
> > > > On Thu, May 12, 2022 at 1:48 PM Greg KH <gregkh@linuxfoundation.org> wrote:
> > > > >
> > > > > I'll drop this for now as there are no in-kernel users for this quirk
> > > > > yet.  When there is a need for one, please resubmit it.
> > > 
> > > Hold on; Greg's comment doesn't seem fair.  There are no in-kernel 
> > > users for this quirk because it is meant to be a user API.  (Just as 
> > > there are no in-kernel users for read(2) -- it is there so that 
> > > userspace can call it).
> > 
> > True, but the kernel calls read(2) itself as well in places, it just
> > looks a bit different, kernel_read_file()  :)
> 
> Okay, but you get the point.  :-)
> 
> > > Jose does have users for the new quirk: Anybody with one of the bad 
> > > Bluetooth CSR knockoff chips.  Now I agree; it would be great if there 
> > > was some way to identify them automatically.  But if that's not 
> > > possible, the only alternative is to allow userspace to set the quirk 
> > > flag whenever it knows the quirk is needed.
> > 
> > Is that the case here that we know how to identify this?  I thought
> > Marcel said something else was happening here.
> > 
> > If the bluetooth developers/maintainers say this is needed for some
> > devices to work properly and they will be handled in userspace somehow
> > through a udev rule or the like, I will gladly add this.  But I thought
> > this thread died out as it was determined that this wasn't needed at
> > this point in time which is why I dropped it.
> 
> It's kind of an odd situation.  In ordinary usage the device works okay.  
> But it stops working after it has been exported over usbip; that is what 
> Jose wants to fix.
> 
> Come to think of it, maybe there is a simple workaround.  If userspace 
> resets the device after it is unconfigured, there's a good chance that 
> will get it to start working again.  Jose, can you try this?  There is a 
> usbreset program you can use, floating around on the web.  (Greg, did 
> that program or something like it ever get added to the usbutils 
> package?)

Yes, it is in the usbutils package.  I don't think many distros package
the prebuilt binary, but the .c file can be found here:
	https://github.com/gregkh/usbutils/blob/master/usbreset.c