linux-kernel - Re: [PATCHv2] usb: gadget: get rid of USB_GADGET_DUALSPEED and USB_GADGET

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Date:	Fri, 19 Aug 2011 10:57:32 -0400 (EDT)
From:	Alan Stern <stern@...land.harvard.edu>
To:	Michal Nazarewicz <mina86@...a86.com>
cc:	Sebastian Andrzej Siewior <bigeasy@...utronix.de>,
	Sergei Shtylyov <sshtylyov@...sta.com>,
	Felipe Balbi <balbi@...com>,
	Yang Rui Rui <ruirui.r.yang@...to.com>,
	Greg Kroah-Hartman <gregkh@...e.de>,
	USB list <linux-usb@...r.kernel.org>,
	Kernel development list <linux-kernel@...r.kernel.org>
Subject: Re: [PATCHv2] usb: gadget: get rid of USB_GADGET_DUALSPEED and
 USB_GADGET_SUPERSPEED

On Fri, 19 Aug 2011, Michal Nazarewicz wrote:

> > I don't quite understand that sentence.  However, it is definitely true
> > that all UDC drivers _must_ avoid connecting at speeds that are faster
> > than the usb_gadget_driver's .speed field.
> 
> Yang has brought up an issue that musb_gadget_start() checks if  
> driver->speed
> equals USB_SPEED_HIGH.  This means that if a gadget driver supports super  
> speed
> it'll set driver->speed to USB_SPEED_SUPER and musb_gadget_start() will  
> complain.
> 
> My understanding is that this is a bug in musb driver as it should allow  
> the
> gadget driver to start but never set super speed.

That's right.  It should also allow driver->speed to be USB_SPEED_FULL, 
in which case it should never connect at high speed (see gmidi.c).

Alan Stern

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