linux-kernel - Re: [PATCH v5 1/2] dt-bindings: reserved-memory: Introduce carved-out memory region binding

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Message-ID: <20250627193132.GB4032621-robh@kernel.org>
Date: Fri, 27 Jun 2025 14:31:32 -0500
From: Rob Herring <robh@...nel.org>
To: Maxime Ripard <mripard@...nel.org>
Cc: Saravana Kannan <saravanak@...gle.com>,
	Sumit Semwal <sumit.semwal@...aro.org>,
	Benjamin Gaignard <benjamin.gaignard@...labora.com>,
	Brian Starkey <Brian.Starkey@....com>,
	John Stultz <jstultz@...gle.com>,
	"T.J. Mercier" <tjmercier@...gle.com>,
	Christian König <christian.koenig@....com>,
	Krzysztof Kozlowski <krzk+dt@...nel.org>,
	Conor Dooley <conor+dt@...nel.org>, Andrew Davis <afd@...com>,
	Jared Kangas <jkangas@...hat.com>,
	Mattijs Korpershoek <mkorpershoek@...nel.org>,
	devicetree@...r.kernel.org, linux-kernel@...r.kernel.org,
	linux-media@...r.kernel.org, dri-devel@...ts.freedesktop.org,
	linaro-mm-sig@...ts.linaro.org
Subject: Re: [PATCH v5 1/2] dt-bindings: reserved-memory: Introduce
 carved-out memory region binding

On Tue, Jun 17, 2025 at 02:25:40PM +0200, Maxime Ripard wrote:
> Some parts of the memory can be dedicated to specific purposes and
> exposed as a dedicated memory allocator.
> 
> This is especially useful if that particular region has a particular
> properties the rest of the memory doesn't have. For example, some
> platforms have their entire RAM covered by ECC but for a small area
> meant to be used by applications that don't need ECC, and its associated
> overhead.
> 
> Let's introduce a binding to describe such a region and allow the OS to
> create a dedicated memory allocator for it.
> 
> Signed-off-by: Maxime Ripard <mripard@...nel.org>
> ---
>  .../bindings/reserved-memory/carved-out.yaml       | 49 ++++++++++++++++++++++
>  1 file changed, 49 insertions(+)
> 
> diff --git a/Documentation/devicetree/bindings/reserved-memory/carved-out.yaml b/Documentation/devicetree/bindings/reserved-memory/carved-out.yaml
> new file mode 100644
> index 0000000000000000000000000000000000000000..9ab5d1ebd9ebd9111b7c064fabe1c45e752da83b
> --- /dev/null
> +++ b/Documentation/devicetree/bindings/reserved-memory/carved-out.yaml
> @@ -0,0 +1,49 @@
> +# SPDX-License-Identifier: GPL-2.0-only OR BSD-2-Clause
> +%YAML 1.2
> +---
> +$id: http://devicetree.org/schemas/reserved-memory/carved-out.yaml#
> +$schema: http://devicetree.org/meta-schemas/core.yaml#
> +
> +title: Carved-out Memory Region
> +
> +description: |

Don't need '|'.

> +  Specifies that the reserved memory region has been carved out of the
> +  main memory allocator, and is intended to be used by the OS as a
> +  dedicated memory allocator.

Other than the commit msg, it is completely lost that this is for 
ECC-less memory.

This description applies to CMA area as well. So what's the difference?

> +
> +maintainers:
> +  - Maxime Ripard <mripard@...nel.org>
> +
> +properties:
> +  compatible:
> +    const: carved-out

Isn't everything in reserved-memory a carve out for some purpose. I'm 
not sure if I'd add 'no ECC' or more along the lines of how this is 
used. The latter might be useful on platforms which can't disable ECC or 
don't have ECC at all.

> +
> +  reg:
> +    description: region of memory that is carved out.

Can be multiple regions? If not, need 'maxItems: 1'.


> +
> +allOf:
> +  - $ref: reserved-memory.yaml
> +  - not:
> +      required:
> +        - reusable
> +  - not:
> +      required:
> +        - no-map
> +
> +required:
> +  - compatible
> +  - reg
> +
> +unevaluatedProperties: false
> +
> +examples:
> +  - |
> +    reserved-memory {
> +        #address-cells = <1>;
> +        #size-cells = <1>;
> +
> +        memory@...40000 {
> +            compatible = "carved-out";
> +            reg = <0x12340000 0x00800000>;
> +        };
> +    };
> 
> -- 
> 2.49.0
>