netdev - Re: [cdc_ncm] guidance and help refactoring cdc

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Message-ID: <alpine.LNX.2.20.1506011404550.4550@localhost.localdomain>
Date:	Mon, 1 Jun 2015 14:08:26 +0200 (CEST)
From:	Enrico Mioso <mrkiko.rs@...il.com>
To:	Oliver Neukum <oneukum@...e.com>
cc:	youtux@...il.com, Greg KH <greg@...ah.com>,
	linux-usb@...r.kernel.org, netdev@...r.kernel.org
Subject: Re: [cdc_ncm] guidance and help refactoring cdc_ncm


On Mon, 1 Jun 2015, Oliver Neukum wrote:

==Date: Mon, 1 Jun 2015 14:00:22
==From: Oliver Neukum <oneukum@...e.com>
==To: Enrico Mioso <mrkiko.rs@...il.com>
==Cc: youtux@...il.com, Greg KH <greg@...ah.com>, linux-usb@...r.kernel.org,
==    netdev@...r.kernel.org
==Subject: Re: [cdc_ncm] guidance and help refactoring cdc_ncm
==
==On Mon, 2015-06-01 at 13:41 +0200, Enrico Mioso wrote:
==> Thank you Oliver, thank you all for reading this thread and the attention.
==> For a more detailed discussion and how we got here, you might google for the 
==> thread:
==> "Is this 32-bit NCM?"
==> and
==> "Is this 32-bit NCM?y" (follow up).
==> Where the "y" letter comes from a mistake of mine.
==
==Having read them it looks like the issues of padding and
==sequence numbers are open.
==
==> The specification does only mandate the position of the NTH (header). The rest 
==> can be in any order and position in general. This will work with most devices: 
==> except, of course, those from Huawei.
==
==Indeed. And a redesign for crap devices looks like
==a bad idea.
==
==> Our aggregate looks something like this from my perspective (anyone correct me 
==> in case):
==> NTH: header
==> NDP: contains indexing informations
==> ethernet packet 1
==> ethernet packet 2
==> ...
==> ethernet packet n;
==> 
==> While it should look like:
==> NTH: header
==> ethernet packet 1
==> ethernet packet 2
==> ...
==> ethernet packet n;
==> NDP: contains indexing informations
==> 
==> but, when introducing such a change: you might break other devices now working. 
==> Infact, clearly there are multiple vendors producing NCM device, as you might 
==> also see by looking at the dirver's comments.
==> So in general, we should be able to dynamically change the way in which the 
==> driver order things in the package.
==> and that's why I initially proposed the "redesign".
==
==OK, so the NDP needs to be at the end. However in the old thread
==you state that this requires the NDP to be built between the
==final aggregate and physically transmitting. I think this is a false
==choice. You could just as well copy the NDP around provided you reserve
==enough space at the end of the skb.
Yes, probably you can do so. I am not against anything at this moment.
==
==	Regards
==		Oliver
==
==
==
==
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