linux-kernel - Re: [PATCH v2] of_net: Implement of_get_nvmem_mac

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Date:   Mon, 26 Mar 2018 20:21:42 +0200
From:   Mike Looijmans <mike.looijmans@...ic.nl>
To:     Florian Fainelli <f.fainelli@...il.com>,
        David Miller <davem@...emloft.net>
Cc:     netdev@...r.kernel.org, linux-kernel@...r.kernel.org,
        devicetree@...r.kernel.org, andrew@...n.ch, robh+dt@...nel.org,
        frowand.list@...il.com
Subject: Re: [PATCH v2] of_net: Implement of_get_nvmem_mac_address helper

On 26-03-18 19:05, Florian Fainelli wrote:
> On 03/26/2018 09:58 AM, David Miller wrote:
>> From: Mike Looijmans <mike.looijmans@...ic.nl>
>> Date: Mon, 26 Mar 2018 08:41:29 +0200
>>
>>> It's common practice to store MAC addresses for network interfaces into
>>> nvmem devices. However the code to actually do this in the kernel lacks,
>>> so this patch adds of_get_nvmem_mac_address() for drivers to obtain the
>>> address from an nvmem cell provider.
>>>
>>> This is particulary useful on devices where the ethernet interface cannot
>>> be configured by the bootloader, for example because it's in an FPGA.
>>>
>>> Tested by adapting the cadence macb driver to call this instead of
>>> of_get_mac_address().
>>>
>>> Signed-off-by: Mike Looijmans <mike.looijmans@...ic.nl>
>>> ---
>>> v2: Use of_nvmem_cell_get to avoid needing the assiciated device
>>>      Use void* instead of char*
>>>      Add devicetree binding doc
>>
>> Like Andrew, I think you should add a new interface for getting the MAC
>> address from nvmem.
>>
>> And drivers can call both of them if they want OF device tree and
>> NVMEM probing for MAC addresses.
>>
>> Later you can add a consolidated interface, if necessary, which does
>> both and also take a reference to the MAC address buffer of the driver
>> in order to deal with the resource allocation issues.
> 
> Agreed, also, how does this fit with Alban's patch series here:

Ok, makes sense. I'll cook up a v3.

> 
> https://lkml.org/lkml/2018/3/24/312
> 
> do you depend on those changes at all?
> 

As far as I can tell, there's no dependency, I'm adding an nvmem 
"consumer" while Alban's patch adds a "provider". I'm mainly interested 
in storing the MAC address into an I2C EEPROM, which you can also buy 
with a pre-programmed MAC address in the first 6 bytes, so there's no 
production cost for managing that.


Alban's patch might some day collide with my idea of making hardware 
that has some unique ID into nvmem providers, like 1-wire chips, some 
NOR flash chips (there's the conflict) and various other devices. That 
would allow a board to obtain a random yet constant MAC address without 
any additional hardware. I'll cross that bridge when I find it.


-- 
Mike Looijmans