linux-kernel - Re: [PATCH 1/4] dt-bindings: nvmem: mmio: new binding for MMIO accessible NVMEM devices

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Message-ID: <20230203210654.GA877968-robh@kernel.org>
Date:   Fri, 3 Feb 2023 15:06:54 -0600
From:   Rob Herring <robh@...nel.org>
To:     Rafał Miłecki <zajec5@...il.com>
Cc:     Srinivas Kandagatla <srinivas.kandagatla@...aro.org>,
        Krzysztof Kozlowski <krzysztof.kozlowski+dt@...aro.org>,
        Matthias Brugger <matthias.bgg@...il.com>,
        Kunihiko Hayashi <hayashi.kunihiko@...ionext.com>,
        Masami Hiramatsu <mhiramat@...nel.org>,
        linux-mediatek@...ts.infradead.org,
        linux-arm-kernel@...ts.infradead.org, devicetree@...r.kernel.org,
        linux-kernel@...r.kernel.org,
        Rafał Miłecki <rafal@...ecki.pl>
Subject: Re: [PATCH 1/4] dt-bindings: nvmem: mmio: new binding for MMIO
 accessible NVMEM devices

On Wed, Feb 01, 2023 at 07:47:14AM +0100, Rafał Miłecki wrote:
> From: Rafał Miłecki <rafal@...ecki.pl>
> 
> With the NVMEM layouts binding in place we should now use:
> 1. NVMEM device access bindings
> 2. NVMEM content description bindings
> 
> This binding allows describing NVMEM devices that can be MMIO accessed.
> 
> Signed-off-by: Rafał Miłecki <rafal@...ecki.pl>
> ---
>  .../devicetree/bindings/nvmem/mmio.yaml       | 46 +++++++++++++++++++
>  1 file changed, 46 insertions(+)
>  create mode 100644 Documentation/devicetree/bindings/nvmem/mmio.yaml
> 
> diff --git a/Documentation/devicetree/bindings/nvmem/mmio.yaml b/Documentation/devicetree/bindings/nvmem/mmio.yaml
> new file mode 100644
> index 000000000000..27e3f6142769
> --- /dev/null
> +++ b/Documentation/devicetree/bindings/nvmem/mmio.yaml
> @@ -0,0 +1,46 @@
> +# SPDX-License-Identifier: (GPL-2.0-only OR BSD-2-Clause)
> +%YAML 1.2
> +---
> +$id: http://devicetree.org/schemas/nvmem/mmio.yaml#
> +$schema: http://devicetree.org/meta-schemas/core.yaml#
> +
> +title: MMIO access based NVMEM
> +
> +description: |
> +  This binding describes simple NVMEM devices that can be accessed by using MMIO
> +  (memory-mapped I/O access).
> +
> +  It's a generic solution for providing NVMEM content access. The way of
> +  handling actual content may be device specific and can be described using a
> +  proper layout.

Please add some guidance based on the discussion about when this should 
and shouldn't be used. Specifically, anything with potential write 
accesses should use a device specific compatible and not the generic 
one.

> +
> +maintainers:
> +  - Rafał Miłecki <rafal@...ecki.pl>
> +
> +allOf:
> +  - $ref: nvmem.yaml#
> +
> +properties:
> +  compatible:
> +    const: mmio-nvmem
> +
> +  reg:
> +    maxItems: 1
> +
> +  reg-io-width:
> +    description: |
> +      The size (in bytes) of the IO accesses that should be performed
> +      on the device.
> +    enum: [1, 2, 4, 8]
> +
> +required:
> +  - reg
> +
> +unevaluatedProperties: false
> +
> +examples:
> +  - |
> +    nvmem@...00 {
> +        compatible = "mmio-nvmem";
> +        reg = <0x10000000 0x10000>;
> +    };
> -- 
> 2.34.1
>