linux-kernel - Re: [PATCH 1/2] mtd: spi-nor: sst: register SFDP region into NVMEM framework to read MAC Address

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Message-ID: <84b1def7-fba7-4f29-a49b-d117efe26d26@microchip.com>
Date: Thu, 6 Mar 2025 06:40:10 +0000
From: <Manikandan.M@...rochip.com>
To: <miquel.raynal@...tlin.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>, <richard@....at>,
	<vigneshr@...com>, <devicetree@...r.kernel.org>,
	<linux-arm-kernel@...ts.infradead.org>, <linux-kernel@...r.kernel.org>,
	<linux-mtd@...ts.infradead.org>, <Varshini.Rajendran@...rochip.com>
Subject: Re: [PATCH 1/2] mtd: spi-nor: sst: register SFDP region into NVMEM
 framework to read MAC Address

Hi Miquel,

On 05/03/25 3:52 pm, Miquel Raynal wrote:
> EXTERNAL EMAIL: Do not click links or open attachments unless you know the content is safe
> 
> On 05/03/2025 at 15:31:33 +0530, Manikandan Muralidharan <manikandan.m@...rochip.com> wrote:
> 
>> From: Varshini Rajendran <varshini.rajendran@...rochip.com>
>>
>> EUI identifier and the MAC Address of the Ethernet Interface is stored
>> after the SFDP table of contents starting at address 0x260 in the
>> QSPI memory.
>> Register the entire SFDP region read by the spi-nor (nor->sfdp) into the
>> NVMEM framework and read the MAC Address when requested using the nvmem
>> properties in the DT by the net drivers.
>>
>> In kernel the Ethernet MAC address relied on U-Boot env variables or
>> generated a random address, which posed challenges for boards without
>> on-board EEPROMs or with multiple Ethernet ports.
>> This change ensures consistent and reliable MAC address retrieval from QSPI,
>> benefiting boards like the sama5d29 curiosity and sam9x75 curiosity.
> 
> Do you mean spi-nor have a programmable area in their SFDP table? Isn't
> this supposed to be a read-only area written once in factory?
> 
The SST26VF064BEUI serial quad flash memory is programmed at the factory 
with a globally unique address stored in the SFDP vendor
parameter table and it is permanently write-protected.

https://ww1.microchip.com/downloads/aemDocuments/documents/MPD/ProductDocuments/DataSheets/SST26VF064BEUI-Data-Sheet-DS20006138.pdf

> I am not a big fan of exposing the whole SFDP area. I would suggest to
> expose just the MAC address. You can make use of nvmem layout drivers if
> that is needed.
> 
> Thanks,
> Miquèl

-- 
Thanks and Regards,
Manikandan M.