netdev - Re: [PATCH] of: net: support NVMEM cells with MAC in text format

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Date:   Wed, 29 Dec 2021 13:40:47 +0100
From:   Michael Walle <michael@...le.cc>
To:     zajec5@...il.com
Cc:     andrew@...n.ch, davem@...emloft.net, devicetree@...r.kernel.org,
        hkallweit1@...il.com, kuba@...nel.org,
        linux-kernel@...r.kernel.org, linux@...linux.org.uk,
        netdev@...r.kernel.org, rafal@...ecki.pl, robh+dt@...nel.org,
        Srinivas Kandagatla <srinivas.kandagatla@...aro.org>,
        Michael Walle <michael@...le.cc>
Subject: Re: [PATCH] of: net: support NVMEM cells with MAC in text format

Hi,

> Some NVMEM devices have text based cells. In such cases MAC is stored in
> a XX:XX:XX:XX:XX:XX format. Use mac_pton() to parse such data and
> support those NVMEM cells. This is required to support e.g. a very
> popular U-Boot and its environment variables.
> 
> Signed-off-by: Rafał Miłecki <rafal@...ecki.pl>
> ---
> Please let me know if checking NVMEM cell length (6 B vs. 17 B) can be
> considered a good enough solution. Alternatively we could use some DT
> property to make it explicity, e.g. something like:
> 
> ethernet@...24000 {
> 	compatible = "brcm,amac";
> 	reg = <0x18024000 0x800>;
> 
> 	nvmem-cells = <&mac_addr>;
> 	nvmem-cell-names = "mac-address";
> 	nvmem-mac-format = "text";
> };

Please note, that there is also this proposal, which had such a conversion
in mind:
https://lore.kernel.org/linux-devicetree/20211228142549.1275412-1-michael@walle.cc/

With this patch, there are now two different places where a mac address
format is converted. In of_get_mac_addr_nvmem() and in the imx otp driver.
And both have their shortcomings and aren't really flexible. Eg. this one
magically detects the format by comparing the length, but can't be used for
to swap bytes (because the length is also ETH_ALEN), which apparently is a
use case in the imx otp driver. And having the conversion in an nvmem
provider device driver is still a bad thing IMHO.

I'd really like to see all these kind of transformations in one place.

-michael