Re: [PATCH v2 2/3] dt-bindings: mtd: physmap: Allow using memory-region to access memory resources

From: Rob Herring <robh@kernel.org>
To: Gregory CLEMENT <gregory.clement@bootlin.com>
Cc: "Linus Walleij" <linus.walleij@linaro.org>,
	"Miquel Raynal" <miquel.raynal@bootlin.com>,
	"Richard Weinberger" <richard@nod.at>,
	"Vignesh Raghavendra" <vigneshr@ti.com>,
	"Krzysztof Kozlowski" <krzk+dt@kernel.org>,
	"Conor Dooley" <conor+dt@kernel.org>,
	"Thomas Petazzoni" <thomas.petazzoni@bootlin.com>,
	"Vladimir Kondratiev" <vladimir.kondratiev@mobileye.com>,
	"Benoît Monin" <benoit.monin@bootlin.com>,
	"Théo Lebrun" <theo.lebrun@bootlin.com>,
	devicetree@vger.kernel.org, linux-kernel@vger.kernel.org,
	linux-arm-kernel@lists.infradead.org,
	linux-mtd@lists.infradead.org
Subject: Re: [PATCH v2 2/3] dt-bindings: mtd: physmap: Allow using memory-region to access memory resources
Date: Mon, 24 Nov 2025 21:19:01 -0600	[thread overview]
Message-ID: <20251125031901.GA1580653-robh@kernel.org> (raw)
In-Reply-To: <20251121-mtd-memregion-v2-2-c5535fdcebe4@bootlin.com>

On Fri, Nov 21, 2025 at 04:42:36PM +0100, Gregory CLEMENT 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@bootlin.com>
> ---
>  .../devicetree/bindings/mtd/mtd-physmap.yaml       | 59 +++++++++++++++-------
>  1 file changed, 40 insertions(+), 19 deletions(-)
> 
> diff --git a/Documentation/devicetree/bindings/mtd/mtd-physmap.yaml b/Documentation/devicetree/bindings/mtd/mtd-physmap.yaml
> index 1b375dee83b0c..323e89aacaacd 100644
> --- a/Documentation/devicetree/bindings/mtd/mtd-physmap.yaml
> +++ b/Documentation/devicetree/bindings/mtd/mtd-physmap.yaml
> @@ -13,10 +13,6 @@ description: |
>    Flash chips (Memory Technology Devices) are often used for solid state
>    file systems on embedded devices.
>  
> -allOf:
> -  - $ref: mtd.yaml#
> -  - $ref: /schemas/memory-controllers/mc-peripheral-props.yaml#
> -
>  properties:
>    compatible:
>      oneOf:
> @@ -61,6 +57,8 @@ properties:
>            - jedec-flash
>            - mtd-ram
>            - mtd-rom
> +          - mtd-mem
> +          - mtd-memro
>  
>    reg:
>      description: |
> @@ -116,6 +114,10 @@ properties:
>      minItems: 1
>      maxItems: 8
>  
> +  memory-region:
> +    items:
> +      - description: Memory regions to map into mtd
> +
>    '#address-cells':
>      const: 1
>  
> @@ -129,21 +131,25 @@ properties:
>  
>  required:
>    - compatible
> -  - reg
> -
> -if:
> -  properties:
> -    compatible:
> -      contains:
> -        const: cortina,gemini-flash
> -then:
> -  properties:
> -    syscon:
> -      $ref: /schemas/types.yaml#/definitions/phandle
> -      description:
> -        Phandle to the syscon controller
> -  required:
> -    - syscon
> +
> +allOf:
> +  - $ref: mtd.yaml#
> +  - if:
> +      properties:
> +        compatible:
> +          contains:
> +            enum:
> +              - mtd-mem
> +              - mtd-memro
> +    then:
> +      required:
> +        - memory-region
> +      properties:
> +        addr-gpios: false
> +    else:
> +      $ref: /schemas/memory-controllers/mc-peripheral-props.yaml#
> +      required:
> +        - reg
>  
>  unevaluatedProperties: false
>  
> @@ -223,4 +229,19 @@ examples:
>              reg = <0 0x04000000>;
>          };
>      };
> +
> +  - |
> +    /* An example using mtd-mem */
> +    mem_logs: mem_logs@10000800 {
> +        reg = <0x1 0x0000800 0x0 0x000f800>;
> +        no-map;
> +    };
> +
> +    memlog {
> +        compatible = "mtd-mem";
> +        memory-region = <&mem_log>;
> +        bank-width = <4>;
> +        device-width = <1>;
> +    };

To repeat v1 comment:

> If we do keep this, I'd rather just add the properties below into the
> /reserved-memory node itself. Devices are created for those nodes if
> they have 'compatible'.

To put it another way, see the ramoops binding and copy that.

Rob