linux-kernel - Re: [PATCH 4/4] hwmon: vcnl3020: add hwmon driver for intrusion sensor

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Date:   Wed, 5 May 2021 09:26:42 +0100
From:   Jonathan Cameron <Jonathan.Cameron@...wei.com>
To:     Ivan Mikhaylov <i.mikhaylov@...ro.com>
CC:     Guenter Roeck <linux@...ck-us.net>,
        Jonathan Cameron <jic23@...nel.org>,
        Lars-Peter Clausen <lars@...afoo.de>,
        Peter Meerwald-Stadler <pmeerw@...erw.net>,
        Jean Delvare <jdelvare@...e.com>,
        <linux-kernel@...r.kernel.org>, <linux-iio@...r.kernel.org>,
        <linux-hwmon@...r.kernel.org>
Subject: Re: [PATCH 4/4] hwmon: vcnl3020: add hwmon driver for intrusion
 sensor

On Tue, 4 May 2021 22:46:53 +0300
Ivan Mikhaylov <i.mikhaylov@...ro.com> wrote:

> On Fri, 2021-04-30 at 09:38 -0700, Guenter Roeck wrote:
> > On Fri, Apr 30, 2021 at 06:24:19PM +0300, Ivan Mikhaylov wrote:  
> > > Intrusion status detection via Interrupt Status Register.
> > > 
> > > Signed-off-by: Ivan Mikhaylov <i.mikhaylov@...ro.com>  
> > 
> > I think this should, if at all, be handled using the
> > iio->hwmon bridge (or, in other words, require a solution
> > which is not chip specific).  
> 
> Thanks a lot for suggestion, it's actually looks what's needed here instead of
> this driver. Anyways, there is no IIO_PROXIMITY support inside supported types
> in iio_hwmon.c. Should I add additional case inside this driver for
> IIO_PROXIMITY type?
> 
> > I am also not sure if "proximity" is really appropriate to use
> > for intrusion detection in the sense of hardware monitoring.
> > This would require a proximity sensor within a chassis, which
> > would be both overkill and unlikely to happen in the real world.
> > "Intrusion", in hardware monitoring context, means "someone
> > opened the chassis", not "someone got [too] close".
> >   
> 
> I'm not sure either but it exists :) And it's exactly for this purpose:
> "someone opened the chassis", "how near/far is cover?".
> 

Hmm. So we will have somewhat of an impedance mismatch.

In IIO events are push based (typically interrupt driven).
There is also the issue that we don't currently have in kernel
interfaces to allow drivers like iio-hwmon to use them (there
has never been enough demand though it has been discussed a few
times).   As such we'd need to implement the core support for
that as well.   We might get away with some simplifications that
make this not too painful - e.g. avoid the need to filter events
by stating that a consumer may well get events it's not interested
in and it is up to the consumer to check (a later optimization could
then add filtering similar to what we do for main data flows).

Jonathan