linux-kernel - Re: [PATCH v2 3/3] ARM: dts: microchip: sama5d29_curiosity: Add nvmem-layout in QSPI for EUI48 MAC Address

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Message-ID: <eed1531a-353a-4244-a10a-95e67c8416ae@lunn.ch>
Date: Wed, 26 Mar 2025 14:18:38 +0100
From: Andrew Lunn <andrew@...n.ch>
To: Manikandan Muralidharan <manikandan.m@...rochip.com>
Cc: robh@...nel.org, krzk+dt@...nel.org, conor+dt@...nel.org,
	nicolas.ferre@...rochip.com, alexandre.belloni@...tlin.com,
	claudiu.beznea@...on.dev, tudor.ambarus@...aro.org,
	pratyush@...nel.org, mwalle@...nel.org, miquel.raynal@...tlin.com,
	richard@....at, vigneshr@...com, devicetree@...r.kernel.org,
	linux-arm-kernel@...ts.infradead.org, linux-kernel@...r.kernel.org,
	linux-mtd@...ts.infradead.org
Subject: Re: [PATCH v2 3/3] ARM: dts: microchip: sama5d29_curiosity: Add
 nvmem-layout in QSPI for EUI48 MAC Address

On Wed, Mar 26, 2025 at 12:51:40PM +0530, Manikandan Muralidharan wrote:
> Add nvmem-layout in QSPI to read the EUI48 Mac address by the
> net drivers using the nvmem property.The offset is set to 0x0
> since the factory programmed address is available in the
> resource managed space and the size determine if the requested
> address is of EUI48 (0x6) or EUI-64 (0x8) type.
> This is useful for cases where U-Boot is skipped and the Ethernet
> MAC address is needed to be configured by the kernel
> 
> Signed-off-by: Manikandan Muralidharan <manikandan.m@...rochip.com>
> ---
>  .../arm/boot/dts/microchip/at91-sama5d29_curiosity.dts | 10 ++++++++++
>  1 file changed, 10 insertions(+)
> 
> diff --git a/arch/arm/boot/dts/microchip/at91-sama5d29_curiosity.dts b/arch/arm/boot/dts/microchip/at91-sama5d29_curiosity.dts
> index 35756cc01e68..6c5ff08f0b3f 100644
> --- a/arch/arm/boot/dts/microchip/at91-sama5d29_curiosity.dts
> +++ b/arch/arm/boot/dts/microchip/at91-sama5d29_curiosity.dts
> @@ -478,6 +478,16 @@ flash@0 {
>  		label = "atmel_qspi1";
>  		status = "okay";
>  
> +		nvmem-layout {
> +			compatible = "fixed-layout";
> +			#address-cells = <1>;
> +			#size-cells = <1>;
> +
> +			mac_address_eui48: mac-address@0 {
> +				reg = <0x0 0x6>;
> +			};
> +		};
> +

I've not looked too deeply how this all works. Don't you need a
reference in the ethernet node pointing to this?

And are there ordering issues? Boards used to use the MAC address from
somewhere else now start using this address, causing a change in
behaviour. I would expect somewhere a comment that this MAC address
will be used last, after all other options have been tried, in order
to avoid regressions.

   Andrew