linux-kernel - Re: [PATCH v10 0/7] Add Fieldbus subsystem + support HMS Profinet card

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Message-ID: <293d9421-4a1c-cc12-f3a7-3f6ea3adb6ea@metux.net>
Date:   Wed, 17 Apr 2019 22:13:59 +0200
From:   "Enrico Weigelt, metux IT consult" <lkml@...ux.net>
To:     Andreas Färber <afaerber@...e.de>
Cc:     Sven Van Asbroeck <thesven73@...il.com>,
        Rob Herring <robh+dt@...nel.org>,
        Linus Walleij <linus.walleij@...aro.org>,
        Lee Jones <lee.jones@...aro.org>, mark.rutland@....com,
        treding@...dia.com, David Lechner <david@...hnology.com>,
        noralf@...nnes.org, johan@...nel.org,
        Michal Simek <monstr@...str.eu>, michal.vokac@...ft.com,
        Arnd Bergmann <arnd@...db.de>,
        Greg KH <gregkh@...uxfoundation.org>, john.garry@...wei.com,
        geert+renesas@...der.be, robin.murphy@....com,
        Paul Gortmaker <paul.gortmaker@...driver.com>,
        sebastien.bourdelin@...oirfairelinux.com, icenowy@...c.io,
        Stuart Yoder <stuyoder@...il.com>,
        "J. Kiszka" <jan.kiszka@...mens.com>, maxime.ripard@...tlin.com,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        netdev <netdev@...r.kernel.org>
Subject: Re: [PATCH v10 0/7] Add Fieldbus subsystem + support HMS Profinet
 card

On 17.04.19 19:04, Andreas Färber wrote:

Hi,

> If you see specific conflicts or differences, please explain them> instead of just throwing around bus names. :) Then we can more easily>
discuss whether to make changes to this framework or whether we indeed>
need some fieldbus/iec61158/ subdirectory.

For example, MVB semantically is more similar to can/canopen or even
SNMP than to iec61158. T-bus is logically more a typically network
interface (similar to 802.3 or HDLC), WTB is actually HDCL via RS485.
KNX has similarities to canopen or SNMP. DALI is somewhat similar
to I2C.

Ergo: there're various fieldbus protocols with entirely different
concepts. Distributed process memory like in iec61158 is just one
of them.

> For your RS-485 I don't see > conflict as that'll just go via tty/serial/ and optionally serdev, no?

That's just layer 0/1. Ontop of that there're various protocols.
Some folks do some ASCII-based protocol ontop of that (eg. elevators,
water plants, etc), others put in HDLC (eg. WTB), some do completely
weird things ;-)

> However, I'd be curious how I/O Link might relate to this, it seems to> have no public specifications.
https://io-link.com/de/Download/Download.php
https://io-link.com/share/Downloads/Spec-Interface/IOL-Interface-Spec_10002_V112_Jul13.pdf

> While I do like sockets, they seem more useful for packet-based> communication, which may be an implementation detail of fieldbus_dev>
drivers, but AFAIU that's unrelated to Sven's memory-focused subsystem>
representing a view of the data received, which may be different from>
the last packet received. Also, when a packet is received via socket,
it> gets dequeued, whereas you'll want to access the device's memory
without> restrictions.
okay, if the device always represents the current process memory, w/o
showing the actual communication, then Sven's approach makes sense.


--mtx

-- 
Enrico Weigelt, metux IT consult
Free software and Linux embedded engineering
info@...ux.net -- +49-151-27565287