Re: [PATCH 0/8] gpiolib: add an ioctl() for monitoring line status changes

["Enrico Weigelt, metux IT consult" <lkml@xxxxxxxxx>]

On 29.11.19 13:57, Linus Walleij wrote:

Hi,

> My own pet peeve is the industrial automation and control use
> case: here we have the design space where people today use
> either PLC:s or RaspberryPi's or Beagle boards, or even some
> custom computers.
> 
> For me personally that is a design space we should cover and
> if this helps the RaspberryPi to do that better I'm all for it.

Yeah, I also have clients in that field. The main problem here,
IMHO is their way of thinking: no device abstraction at all, but all
pretty much hardwired for specific installations (also the reason,
why they'll fail miserable on the new IOT field :p). These folks are
still used to the ancient pure PLC way, where there isn't even anything
like an operating system.

IMHO, it's an educational problem: people need to understand that
there're device abstractions for good reasons, and they should respect
and use them. Basically, they have to understand the concept of
modularization and abstractions. IEC 1131-3 obviously isn't made for
that.

For example, take simple heating installation. Pumps won't be controlled
by raw inverter configuration anymore, but rpm or m²/sec. Temp or flow
sensors don't give raw numbers, but degress Kelvin or m^/sec, etc.
In that case, the corresponding subsystem would be IIO - no need to ever
care about gpios, pwms, etc, directly.

Following this modular approach, everything suddenly gets much easier,
eg. replacing a pump by a different model just requires a minor
reconfiguration instead of rewriting huge parts of the plc code.

I've managed to teach this to an Siemens field technician in one evening
with a few beers, so it can't be that hard to understand.

> An especially interesting case is multiple GPIO expanders
> plugged in on pluggable busses such as PCI or USB. I think
> that kind of discoverability and dynamically expandable GPIO
> blocks is something people in the industry are quite keen to
> get.

Smells like a case for oftree overlays ...

> What we need to do is to make it dirt simple to use GPIOs for
> custom hacks and construction of factories and doorstops
> and what not, while at the same time strongly discouraging
> it to be used to manage hardware such as laptops, tablets
> or phones from userspace. That's maybe hard, and we might
> be victims of our own success ...

I contradict. We should encourage industrial/construction folks to
do decently structured, professional engineering - IOW: use
modularization and highlevel drivers, instead of tinkering with
raw gpios directly like a school kid.


--mtx

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Enrico Weigelt, metux IT consult
Free software and Linux embedded engineering
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