On Sat, Jun 01, 2019 at 03:06:59PM +0300, Vladimir Oltean wrote:

PTP frames will reconstruct the full timestamp without waiting for any
meta (they are the meta), while other MAC-trapped frames (STP etc)
will just carry a meaningless skb->cb when passed up the stack.
In retrospect, it would have been amazing if the switch gave me the
meta frames *before* the actual link-local frames that needed the
timestamp.

I didn't follow everything you wrote, but it sounds like you are on
the right track!

Thanks,
Richard