Re: Setting MAC address from I2C EEPROM - debug / commands? (Xilinx)

12 Jun 2023


      On 6/11/23 David Antliff wrote:
...
On 6/11/23 Sean Anderson wrote:
 > On 6/11/23 23:25, David Antliff wrote:
 > > On 11/23/22 Sean Anderson wrote:
 > >>   On 11/22/22 20:23, David Antliff wrote:
[snip]
...
> >  From a little debugging, I see that the call in eth-uclass.c around line 515 returns a null pointer:
 > > 
 > >        p = dev_read_u8_array_ptr(dev, "mac-address", ARP_HLEN);
 > 
 > This is expected. If (local-)mac-address is defined then nvmem_cell_get_by_name/nvmem_cell_read will not be used.
This was the hint I needed to solve this - thank you.
Turns out that PetaLinux (sigh) was injecting the ff:ff:ff... MAC address into the device-tree build, which is where local-mac-address
was coming from. As you mentioned, and as I can now see in eth-uclass.c, the NVMEM subsystem isn't used if either of these
nodes are defined.
Although PetaLinux's own config insists on setting a MAC address, I was able to set it to a blank string which results
in a DT node, but with no value. This seems sufficient to get past the checks for "{local-,}mac-address" and call the NVMEM
functions instead.
project-spec/configs/config:
CONFIG_SUBSYSTEM_ETHERNET_PSU_ETHERNET_3_MAC=""
For anyone else coming across this, here's my final DT snippet:
axi {
        i2c@ff030000 {
            i2c-mux@74 {
                i2c@0 {
                    eeprom@54 {
                        #address-cells = <1>;
                        #size-cells = <1>;
                        compatible = "atmel,24c128";
                        reg = <0x54>;
mac_address: mac-address@23 {
                            reg = <0x23 6>;
                        };
                    };
                };
            };
        };
ethernet@ff0e0000 {
            nvmem-cells = <&mac_address>;
            nvmem-cell-names = "mac-address";
        };
    };
Also, it appears that 'compatible = ... , "nvmem-cells";' on the EEPROM node is not required.
Thank you for the hints!
-- David.