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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
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