linux-kernel - Re: [PATCH 4/4] rtc: isl1208: add support for isl1219 with hwmon for tamper detection

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Message-ID: <20180131105418.GP2809@piout.net>
Date:   Wed, 31 Jan 2018 11:54:18 +0100
From:   Alexandre Belloni <alexandre.belloni@...e-electrons.com>
To:     Guenter Roeck <linux@...ck-us.net>
Cc:     Denis OSTERLAND <denis.osterland@...hl.com>,
        "linux-rtc@...r.kernel.org" <linux-rtc@...r.kernel.org>,
        "a.zummo@...ertech.it" <a.zummo@...ertech.it>,
        "kernel@...gutronix.de" <kernel@...gutronix.de>,
        "mgr@...gutronix.de" <mgr@...gutronix.de>,
        "jdelvare@...e.com" <jdelvare@...e.com>,
        "devicetree@...r.kernel.org" <devicetree@...r.kernel.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH 4/4] rtc: isl1208: add support for isl1219 with hwmon for
 tamper detection

On 30/01/2018 at 06:15:18 -0800, Guenter Roeck wrote:
> On 01/30/2018 03:40 AM, Denis OSTERLAND wrote:
> > Am Dienstag, den 30.01.2018, 11:27 +0100 schrieb Alexandre Belloni:
> > > On 29/01/2018 at 13:59:19 -0800, Guenter Roeck wrote:
> > > > 
> > > > On Wed, Jan 24, 2018 at 10:03:33AM +0100, Michael Grzeschik wrote:
> > > > [ ... ]
> > > > > 
> > > > > > 
> > > > > > > 
> > > > > > > +
> > > > > > > diff --git a/Documentation/hwmon/sysfs-interface b/Documentation/hwmon/sysfs-interface
> > > > > > > index fc337c317c673..a12b3c2b2a18c 100644
> > > > > > > --- a/Documentation/hwmon/sysfs-interface
> > > > > > > +++ b/Documentation/hwmon/sysfs-interface
> > > > > > > @@ -702,6 +702,13 @@ intrusion[0-*]_alarm
> > > > > > >   		the user. This is done by writing 0 to the file. Writing
> > > > > > >   		other values is unsupported.
> > > > > > > +intrusion[0-*]_timestamp
> > > > > > > +		Chassis intrusion detection
> > > > > > > +		YYYY-MM-DD HH:MM:SS UTC (ts.sec): intrusion detected
> > > > > > > +		RO
> > > > > > > +		The corresponding timestamp on which the intrustion
> > > > > > > +		was detected.
> > > > > > > +
> > > > > > Sneaky. Nack. You don't just add attributes to the ABI because you want it,
> > > > > > without serious discussion, and much less so hidden in an RTC driver
> > > > > > (and even less as unparseable attribute).
> > > > > Right; but it was not meant to be sneaky. I should have stick to my first
> > > > > thought and label this patch RFC. Sorry for that.
> > > > > 
> > > > > > 
> > > > > > In addition to that, I consider the attribute unnecessary. The intrusion
> > > > > > already generates an event which should be sufficient for all practical
> > > > > > purposes.
> > > > > Would it make sense in between the other sysfs attributes of this driver?
> > > > > 
> > > > I don't understand what you mean with that, sorry.
> > > > 
> > > >  From an ABI perspective, the attibute doesn't add value since it is
> > > > highly device specific (or at least it is the only chip I am aware of
> > > > which reports such a time stamp). Feel free to add the attribute to the
> > > > driver and document it, but not as part of the hwmon ABI. In that
> > > > case I would be inclined to accept it. However, keep in mind that
> > > > your version, reporting a human readable date/time, would effectively
> > > > preclude it from ever making it into the ABI.
> > > > 
> > > Actually, there are many RTCs that are able to register one or more
> > > timestamps. My plan was to add support for that soon but I was not
> > > planning to do so in the hwmon ABI as this may be used for something
> > > that is not intrusion detection (interval timers for example).
> > What would you suggest?
> > I think about something like this:
> > event[0-*]_timestamp: timestamp in seconds since epoch or empty if not triggered
> > event[0-*]_alarm: 1 if event was triggered, else 0; write 0 to clear event
> 
> Sure, that makes sense if the events are not specifically related
> to intrusion detection. Question is if there would ever be more than one
> or if event_timestamp and event_alarm would be sufficient.
> 

My target is a PCF85363A which supports up to 3 timestamps. SO I'd go
for timestamp[0-*]. This would be empty if it never triggered (or the
timestamp is invalid) writing anything to that file resets the event. I
don't think we need more than one file per timestamp.

-- 
Alexandre Belloni, Free Electrons
Embedded Linux and Kernel engineering
http://free-electrons.com