[PATCH] defconfig: espressobin: enable NET_RANDOM_ETHADDR

Marek Behún marek.behun at nic.cz
Fri Sep 11 18:22:04 CEST 2020

On Fri, 11 Sep 2020 17:52:26 +0200
Andre Heider <a.heider at gmail.com> wrote:

> Hi Marek,
> On 11/09/2020 13:55, Marek Behún wrote:
> > On Wed, 9 Sep 2020 00:38:31 +0200 Pali Rohár <pali at kernel.org>
> > wrote:  
> >> On Tuesday 08 September 2020 08:52:56 Tom Rini wrote:  
> >>> Note that when CONFIG_NET_RANDOM_ETHADDR is set, we only use a
> >>> random MAC address when we haven't found one either on the
> >>> hardware or environment.  
> >>
> >> I know.
> >>  
> >>> It also prints a warning that you are using a random MAC,
> >>> so if it's documented on how to recover the real MAC a user should
> >>> see that warning and fix it.  
> >>
> >> In case you did backup of MAC address or you have MAC address
> >> printed on sticker, you can restore it. If you loaded distribution
> >> U-Boot which erase MAC address and you have not did any backup,
> >> then your MAC address is forever lost.  
> > 
> > On Turris MOX we write the MAC address into OTP of the SOC during
> > manufacturing.
> > 
> > It is possible to write code that burns the MAC address into OTP, I
> > consider this a better option than enabling random MAC address.
> > 
> > Maybe we can enable random MAC address, and if MAC address is not
> > found in environment nor OTP, issue a warning, something like
> >    "WARNING: MAC address lost, please burn the MAC address of your
> > device to OTP with command xyz"
> > 
> > What do you think?  
> if there's a mac stored in otp during manufacturing, that's of course 
> the best solution. There's no need for CONFIG_NET_RANDOM_ETHADDR
> then. But globalscale does not do that.
> Doing it afterwards, so u-boot claiming some otp space for itself,
> and instructing the user how to write to it sounds too
> dangerous/error-prone.
> For me CONFIG_NET_RANDOM_ETHADDR is a knob that should be enabled if 
> there's no mac address stored in a sane way (where saving it just to
> an u-boot env during manufacturing doesn't count as sane, especially
> if the vendor moves the spi env offset around in a firmware update).
> So I think CONFIG_NET_RANDOM_ETHADDR is enough.

I understand Pali's concerns, though.

The thing is that if we enable CONFIG_NET_RANDOM_ETHADDR by default,
many users that have managed to wipe their env won't care about that
they are using randomly generated MAC address and won't solve the issue,
which is again the spirit of correctly configure networks.

If we do not enable CONFIG_NET_RANDOM_ETHADDR, the worst that can
happen is that the device won't boot from network. This will force the
users to solve the issue, which is not that hard
  setenv ethaddr aa:bb:cc:dd:ee:ff (address from the sticker)
If the users boots from SD/eMMC/SATA/USB, Linux won't have problem with
network, since it will generate random MAC address anyway.

The worst case scenario does not look that bad to me if we don't enable

I think the option CONFIG_NET_RANDOM_ETHADDR should be used only by
developers when they are developing on devices that have not yet burned
the MAC addresses, or on some embedded devices that don't have space
for saving a MAC address (no storage for env or anything else, do such
devices exist?).

But it shouldn't be used as a default setting for a device that has
storage where it can store the address.

> But it would be nice if e.g. a board could set specific env vars as 
> indestructible/unwipeable/precious/whatever, which instructs `env 
> default -a` to keep those (which is common after updating the 
> bootloader). Maybe that's an idea worth pursuing?

Yes, that would be nice :)

> Thanks,
> Andre


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