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Message-ID: <Z9lYA9yUx62wNISq@pengutronix.de> Date: Tue, 18 Mar 2025 12:24:51 +0100 From: Oleksij Rempel <o.rempel@...gutronix.de> To: Matti Vaittinen <mazziesaccount@...il.com> 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 v7 7/7] Documentation: Add sysfs documentation for PSCRR reboot reason tracking On Tue, Mar 18, 2025 at 01:17:38PM +0200, Matti Vaittinen wrote: > 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) ack > Maybe adding a note that not all values are supported on all systems. Yes, there is after supported values. > > > + > > + 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. Yes, there is already: "Importantly, the order of these values **must remain stable**, as bootloaders, user-space tools, or post-mortem investigation utilities may rely on their numerical representation for consistent behavior." :) > > + > > +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 > > -- Pengutronix e.K. | | Steuerwalder Str. 21 | http://www.pengutronix.de/ | 31137 Hildesheim, Germany | Phone: +49-5121-206917-0 | Amtsgericht Hildesheim, HRA 2686 | Fax: +49-5121-206917-5555 |
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