netdev - Re: [PATCH REBASED 2/2] dt-bindings: nvmem: cells: add MAC address cell

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Date:   Tue, 1 Feb 2022 09:55:22 -0600
From:   Rob Herring <robh@...nel.org>
To:     Rafał Miłecki <zajec5@...il.com>
Cc:     Srinivas Kandagatla <srinivas.kandagatla@...aro.org>,
        Michael Walle <michael@...le.cc>,
        linux-mtd@...ts.infradead.org, devicetree@...r.kernel.org,
        linux-kernel@...r.kernel.org, linux-arm-kernel@...ts.infradead.org,
        netdev@...r.kernel.org, Miquel Raynal <miquel.raynal@...tlin.com>,
        Richard Weinberger <richard@....at>,
        Vignesh Raghavendra <vigneshr@...com>,
        Shawn Guo <shawnguo@...nel.org>, Li Yang <leoyang.li@....com>,
        Frank Rowand <frowand.list@...il.com>,
        "David S . Miller" <davem@...emloft.net>,
        Jakub Kicinski <kuba@...nel.org>,
        Ansuel Smith <ansuelsmth@...il.com>,
        Andrew Lunn <andrew@...n.ch>,
        Florian Fainelli <f.fainelli@...il.com>,
        Hauke Mehrtens <hauke@...ke-m.de>,
        Rafał Miłecki <rafal@...ecki.pl>
Subject: Re: [PATCH REBASED 2/2] dt-bindings: nvmem: cells: add MAC address
 cell

On Wed, Jan 26, 2022 at 08:07:45AM +0100, Rafał Miłecki wrote:
> From: Rafał Miłecki <rafal@...ecki.pl>
> 
> This adds support for describing details of NVMEM cell containing MAC
> address. Those are often device specific and could be nicely stored in
> DT.
> 
> Initial documentation includes support for describing:
> 1. Cell data format (e.g. Broadcom's NVRAM uses ASCII to store MAC)
> 2. Reversed bytes flash (required for i.MX6/i.MX7 OCOTP support)
> 3. Source for multiple addresses (very common in home routers)
> 
> Signed-off-by: Rafał Miłecki <rafal@...ecki.pl>
> ---
>  .../bindings/nvmem/cells/mac-address.yaml     | 94 +++++++++++++++++++
>  1 file changed, 94 insertions(+)
>  create mode 100644 Documentation/devicetree/bindings/nvmem/cells/mac-address.yaml
> 
> diff --git a/Documentation/devicetree/bindings/nvmem/cells/mac-address.yaml b/Documentation/devicetree/bindings/nvmem/cells/mac-address.yaml
> new file mode 100644
> index 000000000000..f8d19e87cdf0
> --- /dev/null
> +++ b/Documentation/devicetree/bindings/nvmem/cells/mac-address.yaml
> @@ -0,0 +1,94 @@
> +# SPDX-License-Identifier: GPL-2.0-only OR BSD-2-Clause
> +%YAML 1.2
> +---
> +$id: http://devicetree.org/schemas/nvmem/cells/mac-address.yaml#
> +$schema: http://devicetree.org/meta-schemas/core.yaml#
> +
> +title: NVMEM cell containing a MAC address
> +
> +maintainers:
> +  - Rafał Miłecki <rafal@...ecki.pl>
> +
> +properties:
> +  compatible:
> +    const: mac-address
> +
> +  format:
> +    description: |
> +      Some NVMEM cells contain MAC in a non-binary format.
> +
> +      ASCII should be specified if MAC is string formatted like:
> +      - "01:23:45:67:89:AB" (30 31 3a 32 33 3a 34 35 3a 36 37 3a 38 39 3a 41 42)
> +      - "01-23-45-67-89-AB"
> +      - "0123456789AB"
> +    enum:
> +      - ascii
> +
> +  reversed-bytes:
> +    type: boolean
> +    description: |
> +      MAC is stored in reversed bytes order. Example:
> +      Stored value: AB 89 67 45 23 01
> +      Actual MAC: 01 23 45 67 89 AB
> +
> +  base-address:
> +    type: boolean
> +    description: |
> +      Marks NVMEM cell as provider of multiple addresses that are relative to
> +      the one actually stored physically. Respective addresses can be requested
> +      by specifying cell index of NVMEM cell.

While a base address is common, aren't there different ways the base is 
modified. 

The problem with these properties is every new variation results in a 
new property and the end result is something not well designed. A unique
compatible string, "#nvmem-cell-cells" and code to interpret the data is 
more flexible.

For something like this to fly, I need some level of confidence this is 
enough for everyone for some time (IOW, find all the previous attempts 
and get those people's buy-in). You have found at least 3 cases, but I 
seem to recall more.

Rob