netdev - Re: [RFC][PATCH] net: arinc429: Add ARINC-429 stack

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Date:	Tue, 3 Nov 2015 17:47:54 +0100
From:	Aleksander Morgado <aleksander@...ksander.es>
To:	Marek Vasut <marex@...x.de>
Cc:	Marc Kleine-Budde <mkl@...gutronix.de>,
	Vostrikov Andrey <andrey.vostrikov@...entembedded.com>,
	Oliver Hartkopp <socketcan@...tkopp.net>,
	"netdev@...r.kernel.org" <netdev@...r.kernel.org>,
	"David S. Miller" <davem@...emloft.net>,
	Wolfgang Grandegger <wg@...ndegger.com>,
	Andrew Lunn <andrew@...n.ch>
Subject: Re: [RFC][PATCH] net: arinc429: Add ARINC-429 stack

On Tue, Nov 3, 2015 at 4:19 PM, Marek Vasut <marex@...x.de> wrote:
>> >>>>> I was thinking about this and I mostly agree with you. Obviously,
>> >>>>> copying the code this way was dumb. On the other hand, ARINC and CAN
>> >>>>> are two different sort of busses, so I'd propose something slightly
>> >>>>> different here to avoid confusion and prevent the future extensions
>> >>>>> (or protocols) from adding unrelated cruft into the CAN stack.
>> >>
>> >> I'd keep them separate not because ARINC may add unrelated cruft into
>> >> the CAN stack, but because ARINC is much simpler than CAN already...
>> >
>> > What about maintainability? Why take care of two almost identical
>> > subsystems? With making one stack "simpler" you increase, from my point
>> > of view, the costs of maintaining even more. If you fix problems in one
>> > stack you have to adopt the other, too.
>>
>> If they can share common code, that's fine, that probably can be
>> worked around if needed. My main issues are actually with all the
>> behavior that CAN supports and doesn't make much sense in ARINC, like
>> the complex ID filtering scheme for example (ARINC just requires 256
>> bits for a minimum filter)
>
> So does CAN, I don't see a problem re-using the filtering infrastructure here.

Aren't CAN IDs more than 8-bit long?

Also, ARINC429 labels are logically identifying the data type of the
value being sent, not a given "node" as CAN IDs are (If I'm not
mistaken, correct me if wrong). A single system (e.g. IRS) will send
multiple different labels (e.g. 310 for Latitude, 311 for
Longitude...) to different consumers (e.g. IFE will read all those).
The way a receiver identifies what system generated a given word (as
the same label may have different meaning if sent by different
systems) is usually by mapping in which RX port the word was received
(or also through the special 377 label which may be used as equipment
ID).

-- 
Aleksander
https://aleksander.es
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