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

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Message-ID: <d2b91530-90ae-2d4f-8940-9d88b68caf2c@roeck-us.net>
Date:   Tue, 30 Jan 2018 06:15:18 -0800
From:   Guenter Roeck <linux@...ck-us.net>
To:     Denis OSTERLAND <denis.osterland@...hl.com>,
        "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

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.

Guenter