linux-kernel - Re: [PATCH v3 3/4] dt-bindings: mtd: physmap: Allow using memory-region to access memory resources

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Message-ID: <CAD++jLn9RdCPXQQi-7z2Pba2od4n5jSvh_7X-e0fUKWC+dfM-A@mail.gmail.com>
Date: Fri, 9 Jan 2026 10:52:15 +0100
From: Linus Walleij <linusw@...nel.org>
To: Gregory CLEMENT <gregory.clement@...tlin.com>
Cc: Rob Herring <robh@...nel.org>, Linus Walleij <linus.walleij@...aro.org>, 
	Miquel Raynal <miquel.raynal@...tlin.com>, Richard Weinberger <richard@....at>, 
	Vignesh Raghavendra <vigneshr@...com>, Krzysztof Kozlowski <krzk+dt@...nel.org>, Conor Dooley <conor+dt@...nel.org>, 
	Thomas Petazzoni <thomas.petazzoni@...tlin.com>, 
	Vladimir Kondratiev <vladimir.kondratiev@...ileye.com>, 
	Benoît Monin <benoit.monin@...tlin.com>, 
	Théo Lebrun <theo.lebrun@...tlin.com>, 
	devicetree@...r.kernel.org, linux-kernel@...r.kernel.org, 
	linux-arm-kernel@...ts.infradead.org, linux-mtd@...ts.infradead.org
Subject: Re: [PATCH v3 3/4] dt-bindings: mtd: physmap: Allow using
 memory-region to access memory resources

Hi Gregory,

thanks for your patch!

On Wed, Jan 7, 2026 at 2:05 PM Gregory CLEMENT
<gregory.clement@...tlin.com> wrote:

> Enable access to memory resources not only via I/O address using reg,
> but also through a portion of main memory using memory-region. To
> achieve this, new compatible strings have been introduced: mtd-mem and
> mtd-memro.
>
> Signed-off-by: Gregory CLEMENT <gregory.clement@...tlin.com>

I have two issues with this patch:

1. It needs a description: telling us when to use this and why, and
what makes it necessary to use these new bindings instead of existing
bindings, like the following:

2. To me this looks suspiciously similar to reserved RAM, "reserved-memory".
Documentation/devicetree/bindings/reserved-memory/phram.yaml
Documentation/devicetree/bindings/nvmem/rmem.yaml
Documentation/devicetree/bindings/reserved-memory/ramoops.yaml

Also see the dtschema reserved-memory:
https://github.com/devicetree-org/dt-schema/blob/main/dtschema/schemas/reserved-memory/reserved-memory.yaml

Why is this using "mtd,*" compatibles? What makes is a
"memory technology device", which is admittedly a loose term but
usually means some kind of persistent memory such as flash. This does
not look persistent at all.

To me it seems more related to specific Linux-lingo around the MTD
subsystem and just happens to be handled inside that subsystem in
Linux. Which means it has nothing to do inside a (OS-neutral) DT binding.

So I'm a bit concerned, but maybe I misunderstood something!

Yours,
Linus Walleij