netdev - Re: [PATCH] net: dsa: mv88e6060: report max mtu 1536

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Message-ID: <YvUOSWxZPXa2JX8o@lunn.ch>
Date:   Thu, 11 Aug 2022 16:12:25 +0200
From:   Andrew Lunn <andrew@...n.ch>
To:     Sergei Antonov <saproj@...il.com>
Cc:     Vladimir Oltean <olteanv@...il.com>, netdev@...r.kernel.org,
        Florian Fainelli <f.fainelli@...il.com>
Subject: Re: [PATCH] net: dsa: mv88e6060: report max mtu 1536

> > > 2: eth0: <BROADCAST,MULTICAST> mtu 1504 qdisc noop qlen 1000
> > >     link/ether 00:00:00:00:00:00 brd ff:ff:ff:ff:ff:ff
> >
> > The DSA master is super odd for starting with an all-zero MAC address.
> > What driver handles this part? Normally, drivers are expected to work
> > with a MAC address provided by the firmware (of_get_mac_address or
> > other, perhaps proprietary, means) and fall back to eth_random_addr()
> > if that is missing.
> 
> eth0 is handled by the CONFIG_ARM_MOXART_ETHER driver. By the way, I
> had to change some code in it to make it work, and I am going to
> submit a patch or two later.
> The driver does not know its MAC address initially. On my hardware it
> is stored in a flash memory chip, so I assign it using "ip link set
> ..." either manually or from an /etc/init.d script. A solution with
> early MAC assignment in the moxart_mac_probe() function is doable. Do
> you think I should implement it?

I would suggest a few patches:

1) Use eth_hw_addr_random() to assign a random MAC address during probe.
2) Remove is_valid_ether_addr() from moxart_mac_open()
3) Add a call to platform_get_ethdev_address() during probe
4) Remove is_valid_ether_addr() from moxart_set_mac_address(). The core does this

platform_get_ethdev_address() will call of_get_mac_addr_nvmem() which
might be able to get your MAC address out of flash, without user space
being involved.

      Andrew