Re: [PATCH v7 7/7] Documentation: Add sysfs documentation for PSCRR reboot reason tracking

[Matti Vaittinen <mazziesaccount@gmail.com>]

On 18/03/2025 11:47, 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@pengutronix.de>
> ---
> changes v7:
> - document expected values
> ---
>   .../ABI/testing/sysfs-kernel-reboot-pscrr     | 79 +++++++++++++++++++
>   1 file changed, 79 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..9aa3df8f2fc7
> --- /dev/null
> +++ b/Documentation/ABI/testing/sysfs-kernel-reboot-pscrr
> @@ -0,0 +1,79 @@
> +What:		/sys/kernel/pscrr/reason
> +Date:		April 2025
> +KernelVersion:  6.15
> +Contact:	Oleksij Rempel <o.rempel@pengutronix.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)

nit:
Now that the 'number' <=> 'reason' relation is fixed, we might drop the 
"may differ" etc. Perhaps just:

		Example usage:
		  Read:
			$ cat /sys/kernel/pscrr/reason
			3   # (Example: Power loss event)

		  Write:
			$ echo 5 > /sys/kernel/pscrr/reason
			# Sets the reason to 5 (Example: User-triggered reboot)

Maybe adding a note that not all values are supported on all systems.


> +
> +		Values are defined in:
> +		  - `include/linux/reboot.h` (enum psc_reason)
> +
> +		Supported Values:
> +		Defined in `include/linux/reboot.h` (enum psc_reason):
> +
> +		+-------+---------------------------+--------------------------+
> +		| Value | Symbol                    | Description              |
> +		+-------+---------------------------+--------------------------+
> +		| 0     | PSCR_UNKNOWN              | Unknown or unspecified   |
> +		|       |                           | power state change reason|
> +		+-------+---------------------------+--------------------------+
> +		| 1     | PSCR_UNDER_VOLTAGE        | Supply voltage drop below|
> +		|       |                           | safe threshold.          |
> +		+-------+---------------------------+--------------------------+
> +		| 2     | PSCR_OVER_CURRENT         | Excessive current draw,  |
> +		|       |                           | potential short circuit. |
> +		+-------+---------------------------+--------------------------+
> +		| 3     | PSCR_REGULATOR_FAILURE    | Failure in voltage       |
> +		|       |                           | regulator, preventing    |
> +		|       |                           | stable power delivery.   |
> +		+-------+---------------------------+--------------------------+
> +		| 4     | PSCR_OVER_TEMPERATURE     | Unsafe system temperature|
> +		|       |                           | detected by sensors.     |
> +		+-------+---------------------------+--------------------------+
> +		| 5     | PSCR_EC_PANIC             | Shutdown/reboot triggered|
> +		|       |                           | by Embedded Controller   |
> +		|       |                           | (EC) panic.              |
> +		+-------+---------------------------+--------------------------+
> +
> +		(Note: The actual reason codes used on a specific system depend
> +		on hardware capabilities and configuration.)

I like this. Nice and clean.

A side note which you can consider if you feel like:
This, as far as I understand, will also make the ABI out of this. So, 
perhaps there should be comments in enum psc_reason and the defines in 
Defined in 'include/linux/reboot.h' that they are part of an ABI, and 
must not be changed? I suppose user-space tools may get unhappy if these 
values change between the kernel versions.

> +
> +What:		/sys/kernel/pscrr/reason_boot
> +Date:		April 2025
> +KernelVersion:  6.15
> +Contact:	Oleksij Rempel <o.rempel@pengutronix.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)
> +
> +		Supported Values:
> +		Same as `/sys/kernel/pscrr/reason` (see above).
> +

All in all, this looks very good to me.

Reviewed-by: Matti Vaittinen <mazziesaccount@gmail.com>

Yours,
	-- Matti