netdev - Re: [PATCH net-next 6/6] net: mvpp2: Consider NVMEM cells as possible MAC address source

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Date:   Mon, 21 Nov 2022 10:29:28 +0100
From:   Miquel Raynal <miquel.raynal@...tlin.com>
To:     Marcin Wojtas <mw@...ihalf.com>
Cc:     Rob Herring <robh+dt@...nel.org>,
        Krzysztof Kozlowski <krzk+dt@...nel.org>,
        devicetree@...r.kernel.org,
        "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,
        Russell King <linux@...linux.org.uk>,
        Taras Chornyi <tchornyi@...vell.com>,
        linux-kernel@...r.kernel.org,
        Robert Marko <robert.marko@...tura.hr>,
        Luka Perkov <luka.perkov@...tura.hr>,
        Thomas Petazzoni <thomas.petazzoni@...tlin.com>,
        Michael Walle <michael@...le.cc>
Subject: Re: [PATCH net-next 6/6] net: mvpp2: Consider NVMEM cells as
 possible MAC address source

Hi Marcin,

mw@...ihalf.com wrote on Sat, 19 Nov 2022 09:18:34 +0100:

> Hi Miquel,
> 
> 
> czw., 17 lis 2022 o 22:56 Miquel Raynal <miquel.raynal@...tlin.com> napisał(a):
> >
> > 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  
> 
> Thanks for the patch. Did you manage to test in on a real HW? I am curious about

Yes, I have a Replica switch on which the commercial ports use the
replica PCI IP while the config "OOB" port is running with mvpp2:
[   16.737759] mvpp2 f2000000.ethernet eth52: Using nvmem cell mac address 18:be:92:13:9a:00

> > Signed-off-by: Miquel Raynal <miquel.raynal@...tlin.com>
> > ---
> >  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)) {  
> 
> Unfortunately, nvmem cells seem to be not supported with ACPI yet, so
> we cannot extend fwnode_get_mac_address - I think it should be,
> however, an end solution.

Agreed.

> As of now, I'd prefer to use of_get_mac_addr_nvmem directly, to avoid
> parsing the DT again (after fwnode_get_mac_address) and relying
> implicitly on falling back to nvmem stuff (currently, without any
> comment it is not obvious).

I did not do that in the first place because of_get_mac_addr_nvmem()
was not exported, but I agree it would be the cleanest (and quickest)
approach, so I'll attempt to export the function first, and then use it
directly from the driver.

> Best regards,
> Marcin
> 
> > +               *mac_from = "nvmem cell";
> > +               eth_hw_addr_set(dev, hw_mac_addr);
> > +               return;
> > +       }
> > +
> >         *mac_from = "random";
> >         eth_hw_addr_random(dev);
> >  }
> > --
> > 2.34.1
> >  

Thanks a lot,
Miquèl