Messages in this thread | | | Date | Fri, 21 Jan 2022 04:38:09 +0100 | From | Andrew Lunn <> | Subject | Re: [PATCH RFC V1 net-next 3/4] net: Let the active time stamping layer be selectable. |
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> This is also the reason why DSA denies PTP timestamping on the master > interface, although there isn't any physical reason to do that. For the > same reason mentioned earlier, it would be nice to see hwtstamps for a > packet as it traverses DSA master -> DSA switch port -> PHY attached to > DSA switch.
Don't forget there could be back to back PHYs between the master and the DSA switch port. In theory they could also be doing time stamping.
Also consider the case of a switch port connected to a PHY which does media conversion to SFP. And the SFP has a copper module, so contains another PHY. So you could have the MAC and both PHYs doing time stamping?
So in the extreme case, you have 7 time stamps, 3 from MACs and 4 from PHYs!
I doubt we want to support this, is there a valid use case for it?
Andrew
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