Provider: mjm wired (Mauriat Miranda) While PMBus commands are standardized, there are no mandatory commands, and manufacturers can add as many non-standard commands as they like. Also, different PMBUs devices act differently if non-supported commands are executed. Some devices return an error, some devices return 0xff or 0xffff and set a status error flag, and some devices may simply hang up. Despite all those difficulties, a generic PMBus device driver is still useful and supported since Linux kernel version 2.6.39. However, it was necessary to support device specific extensions in addition to the core PMBus driver, since it is simply unknown what new device specific functionality PMBus device developers come up with next.