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

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Message-ID: <a8f76dd0-56be-46a5-9cc1-2d17d013127d@gmail.com>
Date: Fri, 14 Mar 2025 15:38:55 +0200
From: Matti Vaittinen <mazziesaccount@...il.com>
To: Oleksij Rempel <o.rempel@...gutronix.de>,
 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>
Cc: 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 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?

> +
> +What:		/sys/kernel/pscrr/reason_boot
> +Date:		April 2025
> +KernelVersion:  6.15
> +Contact:	Oleksij Rempel <o.rempel@...gutronix.de>
> +Description:
> +		This file provides the last recorded power state change reason
> +		from before the current system boot. If a supported backend
> +		(e.g., NVMEM) is configured, this value is retained across
> +		reboots.
> +
> +		Example usage (values are for illustration and may not reflect
> +		actual reasons used in a given system):
> +		  Read:
> +			$ cat /sys/kernel/pscrr/reason_boot
> +			2   # (Example: Over-temperature shutdown, may differ per system)
> +