linux-kernel - Re: [PATCH] ethernet: aquantia: Try MAC address from device tree

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Date:   Tue, 30 Nov 2021 03:32:10 +0100
From:   Andrew Lunn <andrew@...n.ch>
To:     Hector Martin <marcan@...can.st>
Cc:     Tianhao Chai <cth451@...il.com>,
        Igor Russkikh <irusskikh@...vell.com>,
        "David S. Miller" <davem@...emloft.net>,
        Jakub Kicinski <kuba@...nel.org>, netdev@...r.kernel.org,
        linux-kernel@...r.kernel.org, Sven Peter <sven@...npeter.dev>,
        Alyssa Rosenzweig <alyssa@...enzweig.io>
Subject: Re: [PATCH] ethernet: aquantia: Try MAC address from device tree

On Mon, Nov 29, 2021 at 02:08:28AM +0900, Hector Martin wrote:
> On 29/11/2021 01.33, Andrew Lunn wrote:
> > On Sat, Nov 27, 2021 at 08:37:33PM -0600, Tianhao Chai wrote:
> > > Apple M1 Mac minis (2020) with 10GE NICs do not have MAC address in the
> > > card, but instead need to obtain MAC addresses from the device tree. In
> > > this case the hardware will report an invalid MAC.
> > > 
> > > Currently atlantic driver does not query the DT for MAC address and will
> > > randomly assign a MAC if the NIC doesn't have a permanent MAC burnt in.
> > > This patch causes the driver to perfer a valid MAC address from OF (if
> > > present) over HW self-reported MAC and only fall back to a random MAC
> > > address when neither of them is valid.
> > 
> > This is a change in behaviour, and could cause regressions. It would
> > be better to keep with the current flow. Call
> > aq_fw_ops->get_mac_permanent() first. If that does not give a valid
> > MAC address, then try DT, and lastly use a random MAC address.
> 
> On DT platforms, it is expected that the device tree MAC will override
> whatever the device thinks is its MAC address.

Can you point to any documentation of that expectation?

> I would not expect any other existing platform to have a MAC assigned to the
> device in this way using these cards; if any platforms do, chances are they
> intended it for it to be used and this patch will fix a current bug. If some
> platforms out there really have bogus MACs assigned in this way, that's a
> firmware bug, and we'd have to find out and add explicit, targeted
> workaround code. Are you aware of any such platforms? :)

I'm not aware of any, because i try to avoid making behaviour changes.

Anyway, lets go with this, and if stuff breaks we can always change
the order to what i suggested in order to unbreak stuff. I'm assuming
for Apple M1 Mac minis the order does not actually matter?

    Andrew