On Mon, 13 Mar 2023 09:40:59 +0100
Oleksij Rempel [off-list ref] wrote:

quoted

But, as you point out, with Köry's/Richard's proposal, the MAC driver
will be bypassed when the selected timestamping layer is the PHY, and
that's a problem currently.

May I suggest the following? There was another RFC which proposed the
introduction of a netdev notifier when timestamping is turned on/off:
https://lore.kernel.org/netdev/20220317225035.3475538-1-vladimir.oltean@nxp.com/ (local)

If we have a notifier, then we can make switch drivers do things
differently. They can activate timestamping per se in the timestamping
NDO (which is only called when the MAC is the active timestamping layer),
and they can activate PTP traps in the netdev notifier (which is called
any time a timestamping status change takes place - the notifier info
should contain details about which net_device and timestamping layer
this is, for example).

It's just a proposal of how to create an alternative notification path
that doesn't disturb the goals of this patch set. 

I will take a look at your patch but indeed adding a timestamp notifier could
be a good idea.

To make things even more complicated - I  have a project where the DSA master
should be used for time stamping. Due to board specific limitations, we
are forced to use FEC PHC instead of dsa KSZ switch PHC. So, it is not
a choice between MAC and PHY, it is more the MAC before MAC and PHY.
PTP sync in this case will have more jitter, but it still good enough
for this project.
Currently I use quick hack to do so, but mainlinamble solution working for
most use cases will be nice.

In this case it is not a PHY/MAC PTP choice anymore but more a device
PTP choice which bring a lot more of complexity. Or maybe we could simply add a
"switch" timestamp layer later on. As Andrew said we will maybe increase the
number of timestamp layers in the future.

Regards,
Köry