linux-kernel - Re: [PATCHv6 net-next 6/7] net: ibm: emac: generate random MAC if not found

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Message-ID: <20241016073637.GE2162@kernel.org>
Date: Wed, 16 Oct 2024 08:36:37 +0100
From: Simon Horman <horms@...nel.org>
To: Rosen Penev <rosenp@...il.com>
Cc: netdev@...r.kernel.org, "David S. Miller" <davem@...emloft.net>,
	Eric Dumazet <edumazet@...gle.com>,
	Jakub Kicinski <kuba@...nel.org>, Paolo Abeni <pabeni@...hat.com>,
	Andrew Lunn <andrew@...n.ch>,
	Shannon Nelson <shannon.nelson@....com>,
	Uwe Kleine-König <u.kleine-koenig@...libre.com>,
	Breno Leitao <leitao@...ian.org>,
	Jeff Johnson <quic_jjohnson@...cinc.com>,
	Christian Marangi <ansuelsmth@...il.com>,
	open list <linux-kernel@...r.kernel.org>
Subject: Re: [PATCHv6 net-next 6/7] net: ibm: emac: generate random MAC if
 not found

On Tue, Oct 15, 2024 at 12:44:52PM -0700, Rosen Penev wrote:
> On Sat, Oct 12, 2024 at 6:16 AM Simon Horman <horms@...nel.org> wrote:
> >
> > On Fri, Oct 11, 2024 at 12:56:21PM -0700, Rosen Penev wrote:
> > > On this Cisco MX60W, u-boot sets the local-mac-address property.
> > > Unfortunately by default, the MAC is wrong and is actually located on a
> > > UBI partition. Which means nvmem needs to be used to grab it.
> > >
> > > In the case where that fails, EMAC fails to initialize instead of
> > > generating a random MAC as many other drivers do.
> > >
> > > Match behavior with other drivers to have a working ethernet interface.
> > >
> > > Signed-off-by: Rosen Penev <rosenp@...il.com>
> > > ---
> > >  drivers/net/ethernet/ibm/emac/core.c | 9 ++++++---
> > >  1 file changed, 6 insertions(+), 3 deletions(-)
> > >
> > > diff --git a/drivers/net/ethernet/ibm/emac/core.c b/drivers/net/ethernet/ibm/emac/core.c
> > > index b9ccaae61c48..faa483790b29 100644
> > > --- a/drivers/net/ethernet/ibm/emac/core.c
> > > +++ b/drivers/net/ethernet/ibm/emac/core.c
> > > @@ -2937,9 +2937,12 @@ static int emac_init_config(struct emac_instance *dev)
> > >
> > >       /* Read MAC-address */
> > >       err = of_get_ethdev_address(np, dev->ndev);
> > > -     if (err)
> > > -             return dev_err_probe(&dev->ofdev->dev, err,
> > > -                                  "Can't get valid [local-]mac-address from OF !\n");
> > > +     if (err == -EPROBE_DEFER)
> > > +             return err;
> > > +     if (err) {
> > > +             dev_warn(&dev->ofdev->dev, "Can't get valid mac-address. Generating random.");
> > > +             eth_hw_addr_random(dev->ndev);
> > > +     }
> >
> > The above seems to take the random path for all errors other than
> > -EPROBE_DEFER. That seems too broad to me, and perhaps it would
> > be better to be more specific. Assuming the case that needs
> > to be covered is -EINVAL (a guess on my part), perhaps something like this
> > would work? (Completely untested!)
> >
> >         err = of_get_ethdev_address(np, dev->ndev);
> >         if (err == -EINVAL) {
> >                 /* An explanation should go here, mentioning Cisco MX60W
> >                  * Maybe the logic should even be specific to that hw?
> >                  */
> >                 dev_warn(&dev->ofdev->dev, "Can't get valid mac-address. Generating random.");
> >                 eth_hw_addr_random(dev->ndev);
> >         } else if (err) {
> >                 return dev_err_probe(&dev->ofdev->dev, err,
> >                                      "Can't get valid [local-]mac-address from OF !\n");
> >         }
> That's just yak shaving. besides 0 and EPROBE_DEFER,
> of_get_ethdev_address returns ENODEV, EINVAL, and maybe something
> else. I don't see a good enough reason to diverge from convention
> here. This same pattern is present in other drivers.

I assumed that more specific error detection would be appropriate, because
it seemed to be a rather specific case.  But if the pattern is present in
other drivers, then that is fine.

> >
> > Also, should this be a bug fix with a Fixes tag for net?
> No. It's more of a feature honestly.
> >
> > >
> > >       /* IAHT and GAHT filter parameterization */
> > >       if (emac_has_feature(dev, EMAC_FTR_EMAC4SYNC)) {
> > > --
> > > 2.47.0
> > >
>