However, from a quick glance at ethtool(8), there appear to be a number of options to query the driver to see what functionality is supported.  So perhaps not a matter of unsupported hardware, but an unsupported feature?

we're currently setting up new hardware with Linux (Devuan Ascii / Debian 9) on Atom Denverton SoC systems utilizing the X553 NICs.

While general networking seems to work just fine, our go-to method to identify the NICs by LEDs blinking (ethtool -p / --identify ethX) doesn't seem to do anything. The command is being accepted (on unsupported hardware we'd get a "Operation not supported"), but there's simply no blinking happening :-(

Various other Intel NICs in use (older chipsets using the e1000 or igb drivers, for example 82574L or I350) display the expected behavior. We've tried the newest drivers 5.3.7. as well as the ones shipped with our kernel of choice (4.16. from backports) - neither seem to work.

Are we doing it wrong? Any hints appreciated :-)