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

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Date:   Tue, 30 Jan 2018 11:40:10 +0000
From:   Denis OSTERLAND <denis.osterland@...hl.com>
To:     "linux@...ck-us.net" <linux@...ck-us.net>,
        "alexandre.belloni@...e-electrons.com" 
        <alexandre.belloni@...e-electrons.com>
CC:     "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

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
> 
> 
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