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

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Message-ID: <Z9Q4z2dPdpqVcu6u@pengutronix.de>
Date: Fri, 14 Mar 2025 15:10:23 +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 v6 7/7] Documentation: Add sysfs documentation for PSCRR
 reboot reason tracking

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?
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