On Mon, Jul 05, 2021 at 08:19:30AM +0000, Y.b. Lu wrote:

When several ptp virtual clocks are created, the ptp physical clock is guaranteed for free running.

What I think is, for timestamping, if no flag SOF_TIMESTAMPING_BIND_PHC, the timestamping keeps using ptp physical clock.
If application wants to bind one ptp virtual clock for timestamping, the flag SOF_TIMESTAMPING_BIND_PHC should be set and clock index should be provided.
After all, several ptp virtual clocks created are likely for different timescale/use case. There should be a method for any of applications to select the right one to use.

Does it make sense?

Yes, indeed.  I totally forgot that the user space PTP stack has
network sockets bond to interfaces, and they are completely separate
from the PHC clockid_t.  Need more sleep...

Thanks,
Richard