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In other words it is an >> extension to the classic snoop bit. > > TPHS includes an bit of data on every TLP and the data transits to the > eventual completer. > > It does not have to be a root port. > >> For P2P that is obviously nonsense because we don't have P2P support >> for cached accesses. > > For P2P the TPH data on the TLP will transit to the P2P completer > unchanged. > > It is up to the completer do define what it does with the TPH data. > > Typically root ports in CPUs will use TPH data for cache placement > instructions. But who knows what a P2P device will use it for. > > In Linux the driver that owns the completing address space gets to > specify how the TPH data works based on its own device specific > knowledge. Yeah that's a good point, I should probably rephrase the question. I'm aware of how TPH works by adding the extra ST to the TLP. But my question is how is that useful to a PCIe endpoint? What is the effect of the ST here? I only know about the caching use case for the root complex and that's clearly not the case here. Regards, Christian. > > Jason