linux-kernel - Re: [RFC PATCH v1 7/7] thermal: core: set Power State Change Reason before hw_protection

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Date: Fri, 19 Jan 2024 20:34:41 +0100
From: Oleksij Rempel <o.rempel@...gutronix.de>
To: "Rafael J. Wysocki" <rafael@...nel.org>
Cc: devicetree@...r.kernel.org, Conor Dooley <conor+dt@...nel.org>,
	Daniel Lezcano <daniel.lezcano@...aro.org>,
	Krzysztof Kozlowski <krzysztof.kozlowski+dt@...aro.org>,
	Liam Girdwood <lgirdwood@...il.com>,
	Mark Brown <broonie@...nel.org>, Sebastian Reichel <sre@...nel.org>,
	linux-kernel@...r.kernel.org,
	Søren Andersen <san@...v.dk>,
	Rob Herring <robh+dt@...nel.org>,
	Srinivas Kandagatla <srinivas.kandagatla@...aro.org>,
	kernel@...gutronix.de, linux-pm@...r.kernel.org,
	Zhang Rui <rui.zhang@...el.com>, Lukasz Luba <lukasz.luba@....com>
Subject: Re: [RFC PATCH v1 7/7] thermal: core: set Power State Change Reason
 before hw_protection_shutdown()

On Fri, Jan 19, 2024 at 07:34:26PM +0100, Rafael J. Wysocki wrote:
> On Fri, Jan 19, 2024 at 2:25 PM Oleksij Rempel <o.rempel@...gutronix.de> wrote:
> >
> > Store the state change reason to some black box for later investigation.
> 
> Seriously?
> 
> What black box, where, how this is useful and who is going to use it,
> pretty please.

The 'black box' refers to a non-volatile memory (NVMEM) cell used by the
Power State Change Reasons (PSCR) framework. This cell stores reasons
for sudden power state changes, like voltage drops or over-temperature
events. This data is invaluable for post-mortem analysis to understand
system failures or abrupt shutdowns. It's particularly useful for
systems where PMICs or watchdogs cannot record such events. The data can
inform recovery routines in the bootloader or early kernel stages during
subsequent boots, enhancing system reliability and aiding in debugging
and diagnostics.

Regards,
Oleksij
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