Re: [PATCH v2 01/22] usb: add OTG version number in usb_otg_descriptor

[Roger Quadros <rogerq-l0cyMroinI0@public.gmane.org>]

On Tue, 9 Jun 2015 10:16:23 -0400
Alan Stern <stern-nwvwT67g6+6dFdvTe/nMLpVzexx5G7lz@public.gmane.org> wrote:

> On Tue, 9 Jun 2015, Li Jun wrote:
> 
> > > > -/* USB_DT_OTG (from OTG 1.0a supplement) */
> > > > +/* USB_DT_OTG */
> > > >  struct usb_otg_descriptor {
> > > >  	__u8  bLength;
> > > >  	__u8  bDescriptorType;
> > > >  
> > > >  	__u8  bmAttributes;	/* support for HNP, SRP, etc */
> > > > +	struct bcdOTG otg_rev[0];
> > > 
> > > why not just __le16 bcdOTG here ?
> > 
> > usb_otg_descriptor of OTG 1.0 and 2.0 have different size, if directly add
> > __le16 bcdOTG here, then it cannot used for OTG 1.0.
> > I use a zero length array as Peter suggested here for bcdOTG, then the size
> > of usb_otg_descriptor is still 3(not 5), which is compliant with OTG 1.x, if OTG

where does the memory for the zero length array pointer get allocated then?

> > 2.0 or later, we can use member of otg_rev to add bcdOTG, then the size
> > of usb_otg_descriptor + bcdOTG will be 5, in one word, I want to use existing
> > usb_otg_descriptor struct to cover both OTG 1.x and 2.0
> 
> In the end, you may find it is simpler to use two different 
> structures: usb_otg_descriptor and usb_otg_20_descriptor.  
> Try it and see.
> 

cheers,
-roger
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