BEAGL-BONE-BLACK: Linux MAC ID configuration

Hello,

Please allow a few days to look into this issue.

regards,

Judith

Sure, thank you for the message.

Hello Matt,

the 'ethaddr' environment variable in u-boot will be passed to Linux.

For example in AM62x I can see the MAC address saved as 'ether' in linux.

# In u-boot
=> print ethaddr
ethaddr=f4:84:4c:fc:1c:f0
=>
=> boot

#In Linux kernel
root@am62xx-evm:~# ifconfig
eth0: flags=4163<UP,BROADCAST,RUNNING,MULTICAST>  mtu 1500  metric 1
        inet6 fe80::f684:4cff:fefc:1cf0  prefixlen 64  scopeid 0x20<link>
        ether f4:84:4c:fc:1c:f0  txqueuelen 1000  (Ethernet)
        RX packets 0  bytes 0 (0.0 B)
        RX errors 0  dropped 0  overruns 0  frame 0
        TX packets 24  bytes 4116 (4.0 KiB)
        TX errors 0  dropped 0 overruns 0  carrier 0  collisions 0

Judith

HI Judith,

Thank you for confirming that "ethaddr" is passed from u-boot to Linux kernel. My question is, however, a "ifconfig" shows up a different MAC other than "ethaddr" in Linux.

Is there a configuration (say in device tree) that can be modified to decide which u-boot env variable to be passed to Linux? Or what can cause this issue?

Please advise.

Thank you.

Hello Matt,

I checked again and found that ethaddr comes from (memory map) register address 0x43000200 and 0x43000204. The second MAC address comes from u-boot, it is saved as eth1addr. U-boot reads this MAC address from EEPROM  and sends to Linux kernel. This is why we have a different MAC address for eth2 in Linux Kernel. As far as I know, there should not be anything to modify the MAC address for device tree, but it can be modified in EEPROM.
regards,

Judith

Hi Judith,

Thank you for the answers. Perhaps we are looking at different processors? I am using AM335x and somehow I did not find the device tree settings and places in AM335x reference manual match what you described.

Anyway, I managed to change the device tree:

Disable mac_sw

&mac_sw {
        pinctrl-names = "default", "sleep";
        pinctrl-0 = <&cpsw_default>;
        pinctrl-1 = <&cpsw_sleep>;
        status = "disabled";
};

And enable mac

&mac {
        slaves = <1>;
        pinctrl-names = "default", "sleep";
        pinctrl-0 = <&cpsw_default>;
        pinctrl-1 = <&cpsw_sleep>;
        status = "okay";
};

Then the MAC ID is passed from "ethaddr" to Linux.

So for my educational purpose, could you please help explain what is the difference between mac_sw and mac? Is mac_sw for setting up the host as a switch, and mac just a regular network endpoint? Otherwise, please explain.

Thank you.

Hello Matt,

So sorry, I was looking at another device. Glad you were able to find the source of the problem for AM335x. Now, I know you mentioned you were using an older u-boot 2018, which SDK exactly is it?

On 2018.01 u-boot branch &mac_sw does not exist.

regards,

Judith

Hi Judith,

Thank you for the reply. I will check out the mac_sw more. Since my issue is resolved, I will close this question. I will open another one if I have further questions.

Thank you.