linux-kernel - Re: [PATCH 2/2] ARM: dts: microchip: sama5d29_curiosity: Add nvmem-layout in QSPI to describe EUI48 MAC address region

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Message-Id: <D889HZF97H8U.1UUX54BAVLAC3@kernel.org>
Date: Wed, 05 Mar 2025 11:31:36 +0100
From: "Michael Walle" <mwalle@...nel.org>
To: "Manikandan Muralidharan" <manikandan.m@...rochip.com>,
 <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>, <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 2/2] ARM: dts: microchip: sama5d29_curiosity: Add
 nvmem-layout in QSPI to describe EUI48 MAC address region

On Wed Mar 5, 2025 at 11:01 AM CET, Manikandan Muralidharan wrote:
> Add nvmem-layout in QSPI to describe EUI48 MAC address region.
> This is useful for cases where U-Boot is skipped and the Ethernet
> MAC address is needed to be configured in Linux.
>
> 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 7be215781549..81aca8502195 100644
> --- a/arch/arm/boot/dts/microchip/at91-sama5d29_curiosity.dts
> +++ b/arch/arm/boot/dts/microchip/at91-sama5d29_curiosity.dts
> @@ -480,6 +480,16 @@ flash@0 {
>  		label = "atmel_qspi1";
>  		status = "okay";
>  
> +		nvmem-layout {
> +			compatible = "fixed-layout";
> +			#address-cells = <1>;
> +			#size-cells = <1>;
> +
> +			mac_address_eui48: mac-address@261 {

I don't think the offset should be hardcoded in the device tree.
Apparently it is a property of this very chip (and not backed up by
a JEDEC standard). What happens if the SFDP are changed for this
flash? I.e. The length of the SFDP region changes.

Also, this looks like it is a layout for the SPI flash contents and
not the SFDP, how do you differentiate between these two? Also
please update your device tree to use 'compatible =
"fixed-partitions"'.

-michael

> +				reg = <0x261 0x6>;
> +			};
> +		};



> +
>  		at91bootstrap@0 {
>  			label = "at91bootstrap";
>  			reg = <0x0 0x40000>;