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

On Tue, 9 Jun 2015 10:16:23 -0400
Alan Stern [off-list ref] wrote:

On Tue, 9 Jun 2015, Li Jun wrote:

quoted

quoted

quoted

-/* 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?

quoted

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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