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

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Message-ID: <CAKxU2N87Nqa73M+wda3Phayu5dmkWEMhDXgxz=4bASV_-8D4yQ@mail.gmail.com>
Date: Tue, 15 Oct 2024 12:44:52 -0700
From: Rosen Penev <rosenp@...il.com>
To: Simon Horman <horms@...nel.org>
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 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.
>
> 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
> >