Re: USB CDC ACM -- why is bProtocol required to be nonzero?

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Hi,

On Fri, Dec 11, 2009 at 07:59:56AM -0800, Greg KH wrote:

[bInterfaceProtocol == 0]

> > From what I can see, adding such an entry would be nontrivial, as a zero
> > in this table is effectively regarded as a wildcard.

Disregard that, I have overlooked the flags field. The patch *is*
trivial.

> Does that follow the cdc-acm spec?  That's what we need to follow here.

>From how I interpret the spec, it does; I was hoping on input from
someone who was involved in the decision to implement it the current
way, as they might know better if there are devices we actually want to
ignore (i.e. from a practical point of view).

> If it does, feel free to send a patch.

--- drivers/usb/class/cdc-acm.c.orig	2009-12-11 12:51:15.000000000 +0100
+++ drivers/usb/class/cdc-acm.c	2009-12-11 12:52:05.000000000 +0100
@@ -1521,6 +1521,8 @@
 
 	/* control interfaces with various AT-command sets */
+	{ USB_INTERFACE_INFO(USB_CLASS_COMM, USB_CDC_SUBCLASS_ACM,
+		USB_CDC_PROTO_NONE) },
 	{ USB_INTERFACE_INFO(USB_CLASS_COMM, USB_CDC_SUBCLASS_ACM,
 		USB_CDC_ACM_PROTO_AT_V25TER) },
 	{ USB_INTERFACE_INFO(USB_CLASS_COMM, USB_CDC_SUBCLASS_ACM,
 		USB_CDC_ACM_PROTO_AT_PCCA101) },

   Simon
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