linux-kernel - Re: [PATCH v6 7/7] Documentation: Add sysfs documentation for PSCRR reboot reason tracking

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Message-ID: <a34c14c1-875d-40a4-8019-67f7b9aa4133@gmail.com>
Date: Mon, 17 Mar 2025 10:46:01 +0200
From: Matti Vaittinen <mazziesaccount@...il.com>
To: Oleksij Rempel <o.rempel@...gutronix.de>
Cc: Sebastian Reichel <sre@...nel.org>,
 Srinivas Kandagatla <srinivas.kandagatla@...aro.org>,
 Benson Leung <bleung@...omium.org>, Tzung-Bi Shih <tzungbi@...nel.org>,
 Daniel Lezcano <daniel.lezcano@...aro.org>, kernel@...gutronix.de,
 linux-kernel@...r.kernel.org, Liam Girdwood <lgirdwood@...il.com>,
 Mark Brown <broonie@...nel.org>, "Rafael J. Wysocki" <rafael@...nel.org>,
 Zhang Rui <rui.zhang@...el.com>, Lukasz Luba <lukasz.luba@....com>,
 linux-pm@...r.kernel.org, Søren Andersen <san@...v.dk>,
 Guenter Roeck <groeck@...omium.org>, Ahmad Fatoum <a.fatoum@...gutronix.de>,
 Andrew Morton <akpm@...ux-foundation.org>, chrome-platform@...ts.linux.dev
Subject: Re: [PATCH v6 7/7] Documentation: Add sysfs documentation for PSCRR
 reboot reason tracking

On 14/03/2025 16:10, Oleksij Rempel wrote:
> On Fri, Mar 14, 2025 at 03:38:55PM +0200, Matti Vaittinen wrote:
>> On 14/03/2025 13:36, Oleksij Rempel wrote:
>>> Add documentation for the Power State Change Reason Recorder (PSCRR)
>>> sysfs interface, which allows tracking of system shutdown and reboot
>>> reasons. The documentation provides details on available sysfs entries
>>> under `/sys/kernel/pscrr/`, explaining their functionality, example usage,
>>> and how they interact with different backend storage options (e.g., NVMEM).
>>>
>>> Signed-off-by: Oleksij Rempel <o.rempel@...gutronix.de>
>>> ---
>>>    .../ABI/testing/sysfs-kernel-reboot-pscrr     | 46 +++++++++++++++++++
>>>    1 file changed, 46 insertions(+)
>>>    create mode 100644 Documentation/ABI/testing/sysfs-kernel-reboot-pscrr
>>>
>>> diff --git a/Documentation/ABI/testing/sysfs-kernel-reboot-pscrr b/Documentation/ABI/testing/sysfs-kernel-reboot-pscrr
>>> new file mode 100644
>>> index 000000000000..7cc643f89675
>>> --- /dev/null
>>> +++ b/Documentation/ABI/testing/sysfs-kernel-reboot-pscrr
>>> @@ -0,0 +1,46 @@
>>> +What:		/sys/kernel/pscrr/reason
>>> +Date:		April 2025
>>> +KernelVersion:  6.15
>>> +Contact:	Oleksij Rempel <o.rempel@...gutronix.de>
>>> +Description:
>>> +		This file provides access to the last recorded power state
>>> +		change reason. The storage backend is configurable and, if
>>> +		supported, the reason may be stored persistently in an
>>> +		NVMEM cell or another backend.
>>> +
>>> +		Reading this file returns an integer representing the last
>>> +		recorded shutdown or reboot cause.
>>> +
>>> +		Writing an integer value to this file sets the reason to be
>>> +		stored and recorded for system analysis.
>>> +
>>> +		Example usage (values are for illustration and may not reflect
>>> +		actual reasons used in a given system):
>>> +		  Read:
>>> +			$ cat /sys/kernel/pscrr/reason
>>> +			3   # (Example: Power loss event, may differ per system)
>>> +
>>> +		  Write:
>>> +			$ echo 5 > /sys/kernel/pscrr/reason
>>> +			# Sets the reason to 5 (Example: User-triggered reboot,
>>> +			# this may not be a real value in your system)
>>> +
>>> +		Values are defined in:
>>> +		  - `include/linux/reboot.h` (enum psc_reason)
>>
>> Is it possible to provide the reason (also) as string?
>>
>> I believe we should fix the meaning of the numbers so the ABI is not
>> changing for the users. Hence we could as well document the meaning of the
>> values(?) If I read the suggestion right, we will in any case have
>> predefined set of reasons in the kernel side.
>>
>> Or, am I missing something?
> 
> Yes, it is correct, the values should be fixed for user space. Should
> they be documented in this documentation too?

I believe it could be helpful for both the user-space users and 
potential pscrr provider driver writers. It could also set things to stone.

But, I don't have much experience on the documentation like this so 
please treat this as a suggestion - but do as you see fits best.

Yours,
	-- Matti