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

[Hector Martin]

On 30/11/2021 11.32, Andrew Lunn wrote:
> 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 don't think this is explicitly clarified anywhere, but the DT binding 
says:

> Specifies the MAC address that was assigned to the network device.

It certainly doesn't say this should be a fallback only to be used if 
the device doesn't have some idea of its MAC. Usually you'd expect 
firmware information to override whatever the device's built-in defaults 
are.

> > 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?

Correct, on these machines the burned-in MAC is invalid so it doesn't 
matter.


--
Hector Martin (marcan@xxxxxxxxx)
Public Key: https://mrcn.st/pub