Re: [PATCH v2 3/3] ARM: dts: microchip: sama5d29_curiosity: Add nvmem-layout in QSPI for EUI48 MAC Address
From: Manikandan.M
Date: Thu Mar 27 2025 - 02:03:22 EST
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@xxxxxxxxxxxxx>
>> ---
>> .../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.