usb: gadget: functions: add ftrace export over USB

[Greg Kroah-Hartman <gregkh@linuxfoundation.org>]

On Thu, Mar 21, 2019 at 11:50:04AM +0200, Felipe Balbi wrote:
> > +static struct usb_interface_descriptor ftrace_intf_desc = {
> > +	.bLength		= USB_DT_INTERFACE_SIZE,
> > +	.bDescriptorType	= USB_DT_INTERFACE,
> > +
> > +	.bAlternateSetting	= 0,
> > +	.bNumEndpoints		= 1,
> > +	.bInterfaceClass	= USB_CLASS_VENDOR_SPEC,
> > +	.bInterfaceSubClass	= USB_SUBCLASS_VENDOR_SPEC,
> 
> We *may* be able to use the USB_DEBUG_CLASS here with a vendor protocol
> which we define to be Linux Ftrace. If folks think it would be best,
> then I can go look at the debug class and check whether it would be
> feasible.

I didn't think that that class allowed vendor protocols, but if it does,
sure, that would be nice.

I don't have access to usb-if specs since they kicked Linux out of the
organization, and because of that, I really don't care about their specs
anymore :)

thanks,

greg k-h