linux-kernel - Re: [PATCH v2 07/17] kexec: Add documentation for KHO

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Date: Sun, 31 Dec 2023 19:55:18 -0800
From: Stanislav Kinsburskii <skinsburskii@...ux.microsoft.com>
To: Alexander Graf <graf@...zon.com>
Cc: linux-kernel@...r.kernel.org, linux-trace-kernel@...r.kernel.org,
	linux-mm@...ck.org, devicetree@...r.kernel.org,
	linux-arm-kernel@...ts.infradead.org, kexec@...ts.infradead.org,
	linux-doc@...r.kernel.org, x86@...nel.org,
	Eric Biederman <ebiederm@...ssion.com>,
	"H. Peter Anvin" <hpa@...or.com>, Andy Lutomirski <luto@...nel.org>,
	Peter Zijlstra <peterz@...radead.org>,
	Rob Herring <robh+dt@...nel.org>,
	Steven Rostedt <rostedt@...dmis.org>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Mark Rutland <mark.rutland@....com>,
	Tom Lendacky <thomas.lendacky@....com>,
	Ashish Kalra <ashish.kalra@....com>,
	James Gowans <jgowans@...zon.com>, arnd@...db.de,
	pbonzini@...hat.com, madvenka@...ux.microsoft.com,
	Anthony Yznaga <anthony.yznaga@...cle.com>,
	Usama Arif <usama.arif@...edance.com>,
	David Woodhouse <dwmw@...zon.co.uk>,
	Benjamin Herrenschmidt <benh@...nel.crashing.org>
Subject: Re: [PATCH v2 07/17] kexec: Add documentation for KHO

On Fri, Dec 22, 2023 at 07:35:57PM +0000, Alexander Graf wrote:
> diff --git a/Documentation/kho/concepts.rst b/Documentation/kho/concepts.rst
> new file mode 100644
> index 000000000000..8e4fe8c57865
> --- /dev/null
> +++ b/Documentation/kho/concepts.rst
> @@ -0,0 +1,88 @@
> +.. SPDX-License-Identifier: GPL-2.0-or-later
> +
> +=======================
> +Kexec Handover Concepts
> +=======================
> +
> +Kexec HandOver (KHO) is a mechanism that allows Linux to preserve state -
> +arbitrary properties as well as memory locations - across kexec.
> +
> +It introduces multiple concepts:
> +
> +KHO Device Tree
> +---------------
> +
> +Every KHO kexec carries a KHO specific flattened device tree blob that
> +describes the state of the system. Device drivers can register to KHO to
> +serialize their state before kexec. After KHO, device drivers can read
> +the device tree and extract previous state.
> +
> +KHO only uses the fdt container format and libfdt library, but does not
> +adhere to the same property semantics that normal device trees do: Properties
> +are passed in native endianness and standardized properties like ``regs`` and
> +``ranges`` do not exist, hence there are no ``#...-cells`` properties.
> +
> +KHO introduces a new concept to its device tree: ``mem`` properties. A
> +``mem`` property can inside any subnode in the device tree. When present,

Should it be "property can be" ?

...

> diff --git a/Documentation/kho/usage.rst b/Documentation/kho/usage.rst
> new file mode 100644
> index 000000000000..5efa2a58f9c3
> --- /dev/null
> +++ b/Documentation/kho/usage.rst
> @@ -0,0 +1,57 @@
> +.. SPDX-License-Identifier: GPL-2.0-or-later
> +
> +====================
> +Kexec Handover Usage
> +====================
> +
> +Kexec HandOver (KHO) is a mechanism that allows Linux to preserve state -
> +arbitrary properties as well as memory locations - across kexec.
> +
> +This document expects that you are familiar with the base KHO
> +:ref:`Documentation/kho/concepts.rst <concepts>`. If you have not read
> +them yet, please do so now.
> +
> +Prerequisites
> +-------------
> +
> +KHO is available when the ``CONFIG_KEXEC_KHO`` config option is set to y
> +at compile team. Every KHO producer has its own config option that you

Should it be "at compile time."?