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

From: "Enrico Weigelt, metux IT consult" <lkml@metux.net>
To: Sven Van Asbroeck <thesven73@gmail.com>,
	Oliver Hartkopp <socketcan@hartkopp.net>
Cc: "Andreas Färber" <afaerber@suse.de>,
	"Linus Walleij" <linus.walleij@linaro.org>,
	"Lee Jones" <lee.jones@linaro.org>,
	mark.rutland@arm.com, treding@nvidia.com,
	"David Lechner" <david@lechnology.com>,
	noralf@tronnes.org, johan@kernel.org,
	"Michal Simek" <monstr@monstr.eu>,
	michal.vokac@ysoft.com, "Arnd Bergmann" <arnd@arndb.de>,
	"Greg KH" <gregkh@linuxfoundation.org>,
	john.garry@huawei.com, geert+renesas@glider.be,
	robin.murphy@arm.com,
	"Paul Gortmaker" <paul.gortmaker@windriver.com>,
	sebastien.bourdelin@savoirfairelinux.com, icenowy@aosc.io,
	"Stuart Yoder" <stuyoder@gmail.com>,
	"J. Kiszka" <jan.kiszka@siemens.com>,
	maxime.ripard@bootlin.com,
	"Linux Kernel Mailing List" <linux-kernel@vger.kernel.org>,
	netdev <netdev@vger.kernel.org>
Subject: Re: [PATCH v10 0/7] Add Fieldbus subsystem + support HMS Profinet card
Date: Mon, 29 Apr 2019 15:54:30 +0200	[thread overview]
Message-ID: <2bed794d-4960-df09-df16-e063cc41eaae@metux.net> (raw)
In-Reply-To: <CAGngYiX_xxDWEAbxQ=XeZPYAA+zgQ32U0Ov=CG86yE=6=qTfpg@mail.gmail.com>

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@metux.net -- +49-151-27565287