netdev - Re: Adding support for ARINC429 into the Linux kernel

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Message-Id: <201306192345.31106.arnd@arndb.de>
Date:	Wed, 19 Jun 2013 23:45:30 +0200
From:	Arnd Bergmann <arnd@...db.de>
To:	Guenter Roeck <linux@...ck-us.net>
Cc:	linux-kernel@...r.kernel.org, netdev@...r.kernel.org,
	"David S. Miller" <davem@...emloft.net>,
	"Greg Kroah-Hartman" <gregkh@...uxfoundation.org>
Subject: Re: Adding support for ARINC429 into the Linux kernel

On Wednesday 19 June 2013, Guenter Roeck wrote:
> I have been asked to explore options for adding ARINC 429 support [1]
> into the Linux kernel, primarily to support devices from Holt Integrated
> Circuits [2] (the request is unrelated to the chip manufacturer).
> 
> ARINC429 is a protocol which is widely used in commercial airplanes. 
> 
> There are various chips supporting this protocol available, as well as
> out-of-tree Linux support. The drivers I have looked at implement it
> either as character device or misc device and typically pass raw receive
> data to userspace.
> 
> I can see a number of options for going forward:
> 1) Implement as character device (or possibly misc device) and pass
>    raw data to/from user space
>    1a) Just implement a driver for the specific chips
>    2b) Implement some kind of generic infrastructure
> 2) Implement as network driver with a new address family, similar to,
>    say, AF_CAN.
> 
> Any thoughts / suggestions which approach would be better and, most of all,
> which approach might have a better chance of being accepted upstream ?

Since this is a standard protocol, a driver that just supports a specific
chip (1a) would be the worst option IMHO.

A character device and a network protocol both sound reasonable, but
it really depends on the use cases:

* Does Linux act both as the sender and receiver, or do you want to
  support just one of the cases (which?)?

* Would you expect to always just transfer a single 32-bit word, or
  are there larger chunks of logically contigous data? What are typical
  and maximum sizes for those?

* Would you expect the kernel to filter for specific data on the
  receiver side?

* Would a user space receiver want to always see all data from one
  sender, or only the latest word?

	Arnd
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