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: <906d596b-391b-43ec-8654-38de64f043f1@microchip.com>
Date: Thu, 27 Mar 2025 06:03:05 +0000
From: <Manikandan.M@...rochip.com>
To: <andrew@...n.ch>
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

Hi Andrew Lunn,

On 26/03/25 6:48 pm, Andrew Lunn wrote:
> EXTERNAL EMAIL: Do not click links or open attachments unless you know the content is safe
> 
> 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?
Yes we need a reference to 'mac_address_eui48' using nvmem-cells in the 
Ethernet node, since the sama5d29_curiosity uses a daughter card for PHY 
[1], the DTS properties are defined in overlay files. Here is the quick 
usage of the nvmem ref in the ethernet node:
	macb0 {
		nvmem-cells = <&mac_address_eui48>;
		nvmem-cell-names = "mac-address";
		
		phy {

		};
	};

[1] --> https://www.microchip.com/en-us/development-tool/ev90j04a
> 
> 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.
> 
The order of search is documented in of_get_mac_address() in 
net/core/of_net.c file

The driver attempts to retrieve the MAC address through a hierarchical 
approach: first checking device tree properties, then exploring NVMEM 
cells, followed by the U-Boot 'ethaddr' environment variable. If no 
valid MAC address is found through these methods, the driver will 
generate a random but valid MAC address as a final fallback mechanism.
>     Andrew

-- 
Thanks and Regards,
Manikandan M.