RE: [RFC/PATCH 02/12] usb: gadget: change USB version to USB3.0

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> From: Alan Stern [mailto:stern@xxxxxxxxxxxxxxxxxxx] 
> Sent: Friday, March 18, 2011 6:27 PM
> On Fri, 18 Mar 2011, Paul Zimmerman wrote:
>
> > > --- a/drivers/usb/gadget/audio.c
> > > +++ b/drivers/usb/gadget/audio.c
> > > @@ -52,7 +52,7 @@ static struct usb_device_descriptor device_desc = {
> > >  	.bLength =		sizeof device_desc,
> > >  	.bDescriptorType =	USB_DT_DEVICE,
> > >  
> > > -	.bcdUSB =		__constant_cpu_to_le16(0x200),
> > > +	.bcdUSB =		cpu_to_le16(0x0300),
> > >  
> > >  	.bDeviceClass =		USB_CLASS_PER_INTERFACE,
> > >  	.bDeviceSubClass =	0,
> > 
> > This won't work. Now the gadget will not be recognized by a USB 2.0
> > host.
>
> Why not?  I'm not aware of any hosts that will refuse to work with a 
> device merely because the bcdUSB field says 0x0300 instead of 0x0200.
>
> For that matter, there are plenty of legacy hosts that don't have 
> high-speed USB support.  Their controllers are only at the USB-1.1 
> level, but that doesn't stop them from using USB-2.0 devices at full 
> speed.

Yep, you are right. I just tried it with both a Linux and Windows host,
and they both work.

I guess I was thinking about some compliance test tools we have used. I
know they can be very picky about the contents of the bcsUSB field.

-- 
Paul

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