Re: [PATCH RFC V1 net-next 3/4] net: Let the active time stamping layer be selectable.

From: Grygorii Strashko
Date: Tue Apr 05 2022 - 17:38:34 EST

On 05/04/2022 14:19, Kurt Kanzenbach wrote:
On Tue Apr 05 2022, Michael Walle wrote:
Am 2022-04-05 11:01, schrieb Kurt Kanzenbach:
On Mon Apr 04 2022, Michael Walle wrote:
That would make sense. I guess what bothers me with the current
mechanism is that a feature addition to the PHY in the *future* (the
timestamping support) might break a board - or at least changes the
behavior by suddenly using PHY timestamping.

Currently PHY timestamping is hidden behind a configuration option
(NETWORK_PHY_TIMESTAMPING). By disabling this option the default
behavior should stay at MAC timestamping even if additional features
are added on top of the PHY drivers at later stages. Or not?

That is correct. But a Kconfig option has several drawbacks:
(1) Doesn't work with boards where I might want PHY timestamping
on *some* ports, thus I need to enable it and then stumple
across the same problem.
(2) Doesn't work with generic distro support, which is what is
ARM pushing right now with their SystemReady stuff (among other
things also for embeddem system). Despite that, I have two boards
which are already ready for booting debian out of the box for
example. While I might convince Debian to enable that option
(as I see it, that option is there to disable the additional
overhead) it certainly won't be on a per board basis.
Actually for keeping the MAC timestamping as is, you'd need to
convince a distribution to never enable the PHY timestamping
kconfig option.

So yes, I agree it will work when you have control over your
kconfig options, after all (1) might be more academic. But I'm
really concerned about (2).

Yes, the limitations described above are exactly one of the reasons to
make the timestamping layer configurable at run time as done by these

Seems like PHY TS support belongs to HW description category, so could it be device tree material,
like generic property defining which layer should do timestamping?

Best regards,
Grygorii, Ukraine