linux-kernel - Re: [PATCH 1/2] dt-bindings: nvmem: io: new binding for IO accessible NVMEM devices

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Date:   Mon, 30 Jan 2023 14:32:51 -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>,
        Michael Walle <michael@...le.cc>, devicetree@...r.kernel.org,
        linux-mtd@...ts.infradead.org,
        linux-arm-kernel@...ts.infradead.org, linux-kernel@...r.kernel.org,
        Rafał Miłecki <rafal@...ecki.pl>
Subject: Re: [PATCH 1/2] dt-bindings: nvmem: io: new binding for IO
 accessible NVMEM devices

On Fri, Jan 27, 2023 at 06:58:30PM +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 accessed using
> IO mappings.
> 
> Signed-off-by: Rafał Miłecki <rafal@...ecki.pl>
> ---
>  .../devicetree/bindings/nvmem/io.yaml         | 37 +++++++++++++++++++

What do we call nvmem using ISA/PCI IO space? That was my first thought 
seeing "IO". Probably unlikely, but still. "MMIO" instead?

>  1 file changed, 37 insertions(+)
>  create mode 100644 Documentation/devicetree/bindings/nvmem/io.yaml
> 
> diff --git a/Documentation/devicetree/bindings/nvmem/io.yaml b/Documentation/devicetree/bindings/nvmem/io.yaml
> new file mode 100644
> index 000000000000..67e0aae9cd94
> --- /dev/null
> +++ b/Documentation/devicetree/bindings/nvmem/io.yaml
> @@ -0,0 +1,37 @@
> +# SPDX-License-Identifier: (GPL-2.0-only OR BSD-2-Clause)
> +%YAML 1.2
> +---
> +$id: http://devicetree.org/schemas/nvmem/io.yaml#
> +$schema: http://devicetree.org/meta-schemas/core.yaml#
> +
> +title: IO access based NVMEM
> +
> +description: |
> +  This binding describes simple NVMEM devices that can be accessed by simply
> +  mapping a predefined IO address.
> +
> +  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.

As the accesses are memory-mapped, the child nodes should also have 
memory-mapped addresses. IOW, you need 'ranges', '#address-cells', 
'#size-cells'.

> +
> +maintainers:
> +  - Rafał Miłecki <rafal@...ecki.pl>
> +
> +allOf:
> +  - $ref: nvmem.yaml#
> +
> +properties:
> +  compatible:
> +    const: io-nvmem
> +
> +  reg:
> +    maxItems: 1

The first addition here will be access size restrictions. Perhaps add 
that now (reg-io-width).

> +
> +unevaluatedProperties: false
> +
> +examples:
> +  - |
> +    nvmem@...00 {
> +        compatible = "io-nvmem";
> +        reg = <0x10000000 0x10000>;
> +    };
> -- 
> 2.34.1
>