Configuring device TM

P4 excluded TM configuration from its spec. Under P4 RT what are the common methods to configure TM parameters?

That’s out-of-scope of P4Runtime standard Protobuf messages, which target the PSA architecture. PSA doesn’t standardize anything when it comes to configuration of the TM. In theory one could leverage P4Runtime extensions and define new messages to configure the TM: P4Runtime Specification

I did a quick search and found that for Tofino-based platforms, the Stratum NOS lets you configure some TM parameters over gNMI: stratum/ at main · stratum/stratum · GitHub. Maybe something worth looking into.