linux-kernel - Re: RFC: Selecting an NVMEM cell for Power State Change Reason (PSCR) recording

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Message-ID: <202510020904.1E48B7EB@keescook>
Date: Thu, 2 Oct 2025 09:07:44 -0700
From: Kees Cook <kees@...nel.org>
To: Oleksij Rempel <o.rempel@...gutronix.de>
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>,
	Rob Herring <robh@...nel.org>,
	Krzysztof Kozlowski <krzk+dt@...nel.org>,
	Conor Dooley <conor+dt@...nel.org>, Tony Luck <tony.luck@...el.com>,
	"Guilherme G. Piccoli" <gpiccoli@...lia.com>,
	Greg Kroah-Hartman <gregkh@...uxfoundation.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>,
	Matti Vaittinen <mazziesaccount@...il.com>,
	Ahmad Fatoum <a.fatoum@...gutronix.de>,
	Andrew Morton <akpm@...ux-foundation.org>,
	chrome-platform@...ts.linux.dev, devicetree@...r.kernel.org,
	linux-hardening@...r.kernel.org
Subject: Re: RFC: Selecting an NVMEM cell for Power State Change Reason
 (PSCR) recording

On Thu, Oct 02, 2025 at 02:00:09PM +0200, Oleksij Rempel wrote:
> I'm seeking consensus on a minimal, upstream-acceptable way to identify the
> single NVMEM cell used to persist a Power State Change Reason (PSCR). Typical
> targets are battery-backed RTC scratchpads or small EEPROM. The aim is to have
> a tiny breadcrumb available before userspace, across full power cuts, and
> shared by bootloader/kernel/userspace.
> [...]
> * pstore integration (not tried): a backend that uses a nominated NVMEM cell if
>   such a nomination is acceptable.

Several years ago I wanted to have tighter integration between pstore
and nvdimm code. The thread is here, for reference:
https://lore.kernel.org/lkml/CAGXu5jLtmb3qinZnX3rScUJLUFdf+pRDVPjy=CS4KUtW9tLHtw@mail.gmail.com/

I'm not sure it it'll be a useful as background, but I thought I'd
mention it. :)

-Kees

-- 
Kees Cook