[PATCH RFC] cmd: fix net list command

Michael Walle michael at walle.cc
Mon Nov 15 14:46:34 CET 2021

Am 2021-11-15 14:17, schrieb Marek Vasut:
> On 11/15/21 1:24 PM, Michael Walle wrote:
>> Am 2021-11-15 13:15, schrieb Marek Vasut:
>>> On 11/15/21 1:11 PM, Michael Walle wrote:
>>>> Don't get the MAC address by the environment, but by the platform 
>>>> data
>>>> of the udevice. This will fix "net list" if the MAC address is 
>>>> randomly
>>>> generated and won't change behavior when linux is booted.
>>>> Signed-off-by: Michael Walle <michael at walle.cc>
>>>> ---
>>>> Hi,
>>>> this is a proposal to fix the "net list" in a way that linux still 
>>>> can have
>>>> its own fallback mechanism of MAC addresses even if the bootloader 
>>>> has
>>>> The intention is to replace [1], where if I understood correctly, 
>>>> the
>>>> intention was to fix "net list".
>>>> [1] 
>>>> https://lore.kernel.org/u-boot/3996ba2ee4e6ac136c0802dc0df4ef9b1750157c.1635506067.git.michal.simek@xilinx.com/
>>> Does that mean U-Boot and Linux will possibly each have different MAC
>>> address on the same device ? That is clearly wrong and not how it is
>>> supposed to work, U-Boot passes its ethaddr/ethNaddr settings to 
>>> Linux
>>> so that they would have the same MAC address on the same device.
>> Yes they have different ones, but having a random mac address is  
>> wrong
>> in the first place. So IMHO it is more useful to dectect that in 
>> linux,
>> (and there was a good point that usually a user will look at dmesg and
>> not some u-boot output) than having two different random MAC 
>> addresses,
>> one for u-boot and one for linux.
> Currently U-Boot passes MAC address stored in ethaddr/ethNaddr
> variable to Linux by patching it into DT, so Linux has the same MAC
> address, that is the correct behavior.
> If U-Boot generates random MAC address for some reason, then the same
> random MAC address is also passed to Linux.

So, then why does linux have some other means to fix that? Which are
now not available anymore (or doesn't get triggered).

> The argument that user cannot be bothered to look at U-Boot console
> when debugging a problem with random MAC address being passed to Linux
> is bogus, sorry. This is exactly where the user should look and fix
> the problem.
> Are you by any chance trying to work around some bug on your system,
> where U-Boot is unable to obtain the correct MAC address from OTP and
> pass that to Linux, so by ignoring the "ethaddr" variable here, you in
> fact avoid passing that U-Boot MAC address to Linux and Linux uses
> some internal fallback and picks MAC address from OTP itself ?

No I'm not, I try to preserve the initial intention of that random
ethernet address. But anyway. Take this patch or leave it. I'll turn
this option off and open code it into my board file (or just disable
it because I don't actually need it).

>> Initially that random MAC address thing was supposed to get networking
>> running in u-boot if there is no ethaddr at all, eg. for network 
>> console.
>> Now we are passing this made up network address to linux, too. Why?
> We are passing the MAC address used by U-Boot to Linux, it doesn't
> matter whether it is random or not.

And again you're masking the error and possible fixes by linux itself.
Seems like this isn't an argument.

>> Just
>> because it is wrong to have two different mac addresses? Some drivers
>> doesn't even probe without one. And we are just masking away this 
>> error.
>> You get this "two different mac addresses" between reboots. Which is 
>> also
>> wrong. This actually strenghten my opinion that this "feature" should
>> be an u-boot only thing.
> Maybe it would make sense to have U-Boot obtain the correct MAC
> address on your machine first, and then pass that same correct MAC
> address to Linux ?

Eh? I don't get it. That is the only reason to have this option.
Again, this has nothing to do with my board which doesn't have a
MAC address and cannot read it for now (because for now, the user
is expected to set it via the environment). It's about the correct
behavior of the said config option.

Sorry, if the original intention was to make "net list" work
correctly, then why is there now such a huge fuzz around that
CONFIG_NET_RANDOM_ETHADDR config option and why can't we just
fix the error with "net list" and leave the behavior like it
was for years.


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