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Message-ID: <cda899c6-4330-465c-80b2-63c9da73505b@gmail.com>
Date: Tue, 18 Mar 2025 13:17:38 +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 v7 7/7] Documentation: Add sysfs documentation for PSCRR
reboot reason tracking
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@...gutronix.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@...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)
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@...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)
> +
> + Supported Values:
> + Same as `/sys/kernel/pscrr/reason` (see above).
> +
All in all, this looks very good to me.
Reviewed-by: Matti Vaittinen <mazziesaccount@...il.com>
Yours,
-- Matti
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