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

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Message-ID: <CAPv3WKds1gUN1V-AkdhPJ7W_G285Q4PmAbS0_nApPgU+3RK+fA@mail.gmail.com>
Date:   Mon, 21 Nov 2022 15:46:44 +0100
From:   Marcin Wojtas <mw@...ihalf.com>
To:     Miquel Raynal <miquel.raynal@...tlin.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

pon., 21 lis 2022 o 10:29 Miquel Raynal <miquel.raynal@...tlin.com> napisał(a):
>
> 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
>

Nice. Do you have a DT snippet that can possibly be shared? I'd like
to recreate this locally and eventually leverage EDK2 firmware to
expose that.

> > > 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.
>

That would be great, thank you. Please add one-comment in the
mvpp2_main.c, that this is valid for now only in DT world.

Best regards,
Marcin