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

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Message-ID: <2bed794d-4960-df09-df16-e063cc41eaae@metux.net>
Date:   Mon, 29 Apr 2019 15:54:30 +0200
From:   "Enrico Weigelt, metux IT consult" <lkml@...ux.net>
To:     Sven Van Asbroeck <thesven73@...il.com>,
        Oliver Hartkopp <socketcan@...tkopp.net>
Cc:     Andreas Färber <afaerber@...e.de>,
        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 24.04.19 17:10, Sven Van Asbroeck wrote:

> The subsystem is called fieldbus_dev "fieldbus device" because it> abstracts Linux fieldbus clients that want to expose themselves as>
e.g. an actuator, motor, console light, switch, ...
Sounds a bit confusing. With that description, I'd expect highlevel
interfaces similar to LED, input, IIO, etc ... but you're actually
implementing an distributed process memory system. This in turn is
just a subset of the fieldbus world.

> During one of the eleven review cycles, drivers/fieldbus_dev got> truncated to drivers/fieldbus because the reviewers felt that> _dev
was redundant, given the lack of other fieldbus> subsystems.
There is at least one: CAN. Sometimes CAN is used in the IEC61158-way,
but also completely different, even both in combination.

> These cards are not controllers, but slaves on the bus.

Do they really implement the process memory part or just the lower
layer communications ?

> I'm by no means a fieldbus expert. It seems that the term> 'fieldbus' is much broader than these process-memory based> standards?

Yes, indeed.

> I am open to any _concrete_ naming suggestion
> that can get consensus.
Maybe IEC61158 ?

> I'm a bit confused by Wikipedia's entry for fieldbus.
> It suggests that IEC 61158 and Fieldbus are
> interchangeable?
> https://en.wikipedia.org/wiki/Fieldbus

That's wrong.

> <quote>
> Fieldbus is the name of a family of industrial computer
> network protocols used for real-time distributed control,
> standardized as IEC 61158.
> </quote>

IEC 61158 only standardizes one particular approach: the distributed
process memory.

> Given that CAN/EtherCAT are not process memory based
> (that I know of), the fieldbus_dev subsystem is probably
> not a good fit.

ACK. Neither are MVB+friends.


--mtx

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