Possible reason can be :
- "phy_read_mmd" and "phy_write_mmd" are not supported in your kernel version (if version is old).
Possible solution to be evaluated :
- Change "phy_write_mmd" to "phy_write_mmd_indirect" function and do the corresponding changes to support this
- Change "phy_read_mmd" to "phy_read_mmd_indirect" function and do the corresponding changes to support this