netdev - Re: [PATCH 5/5] net: mvpp2: Consider NVMEM cells as possible MAC address source

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Date:   Fri, 28 Oct 2022 15:33:31 +0200
From:   Michael Walle <michael@...le.cc>
To:     Miquel Raynal <miquel.raynal@...tlin.com>
Cc:     Srinivas Kandagatla <srinivas.kandagatla@...aro.org>,
        linux-kernel@...r.kernel.org, Rob Herring <robh+dt@...nel.org>,
        Krzysztof Kozlowski <krzk+dt@...nel.org>,
        devicetree@...r.kernel.org, Marcin Wojtas <mw@...ihalf.com>,
        Russell King <linux@...linux.org.uk>,
        Maxime Chevallier <maxime.chevallier@...tlin.com>,
        "David S. Miller" <davem@...emloft.net>,
        Jakub Kicinski <kuba@...nel.org>,
        Paolo Abeni <pabeni@...hat.com>,
        Eric Dumazet <edumazet@...gle.com>, netdev@...r.kernel.org,
        Robert Marko <robert.marko@...tura.hr>,
        Thomas Petazzoni <thomas.petazzoni@...tlin.com>
Subject: Re: [PATCH 5/5] net: mvpp2: Consider NVMEM cells as possible MAC
 address source

Am 2022-10-28 11:23, schrieb Miquel Raynal:
> The ONIE standard describes the organization of tlv (type-length-value)
> arrays commonly stored within NVMEM devices on common networking
> hardware.
> 
> Several drivers already make use of NVMEM cells for purposes like
> retrieving a default MAC address provided by the manufacturer.
> 
> What made ONIE tables unusable so far was the fact that the information
> where "dynamically" located within the table depending on the
> manufacturer wishes, while Linux NVMEM support only allowed statically
> defined NVMEM cells. Fortunately, this limitation was eventually 
> tackled
> with the introduction of discoverable cells through the use of NVMEM
> layouts, making it possible to extract and consistently use the content
> of tables like ONIE's tlv arrays.
> 
> Parsing this table at runtime in order to get various information is 
> now
> possible. So, because many Marvell networking switches already follow
> this standard, let's consider using NVMEM cells as a new valid source 
> of
> information when looking for a base MAC address, which is one of the
> primary uses of these new fields. Indeed, manufacturers following the
> ONIE standard are encouraged to provide a default MAC address there, so
> let's eventually use it if no other MAC address has been found using 
> the
> existing methods.
> 
> Link: 
> https://opencomputeproject.github.io/onie/design-spec/hw_requirements.html
> Signed-off-by: Miquel Raynal <miquel.raynal@...tlin.com>
> ---
> 
> Hello, I suppose my change is safe but I don't want to break existing
> setups so a review on this would be welcome!
> 
>  drivers/net/ethernet/marvell/mvpp2/mvpp2_main.c | 6 ++++++
>  1 file changed, 6 insertions(+)
> 
> diff --git a/drivers/net/ethernet/marvell/mvpp2/mvpp2_main.c
> b/drivers/net/ethernet/marvell/mvpp2/mvpp2_main.c
> index eb0fb8128096..7c8c323f4411 100644
> --- a/drivers/net/ethernet/marvell/mvpp2/mvpp2_main.c
> +++ b/drivers/net/ethernet/marvell/mvpp2/mvpp2_main.c
> @@ -6104,6 +6104,12 @@ static void mvpp2_port_copy_mac_addr(struct
> net_device *dev, struct mvpp2 *priv,
>  		}
>  	}
> 
> +	if (!of_get_mac_address(to_of_node(fwnode), hw_mac_addr)) {

Mh, the driver already does a fwnode_get_mac_address() which might
fetch it from OF. But that variant doesn't try to get the mac address
via nvmem; in contrast to the of_get_mac_address() variant which will
also try NVMEM.
Maybe it would be better to just use device_get_ethdev_address() and
extend that one to also try the nvmem store. Just to align all the
different variants to get a mac address.

-michael

> +		*mac_from = "nvmem cell";
> +		eth_hw_addr_set(dev, hw_mac_addr);
> +		return;
> +	}
> +
>  	*mac_from = "random";
>  	eth_hw_addr_random(dev);
>  }