On Wed, Jun 05, 2019 at 09:08:54PM +0300, Vladimir Oltean wrote:

Currently I'm using a cyclecounter, but I *will* need actual PHC
manipulations for the time-based shaping and policing features that
the switch has in hardware.

Okay.

On the other hand I get much tighter sync
offset using the free-running counter than with hardware-corrected
timestamps.

Why?  The time stamps come from the very same counter, don't they?

So as far as I see it, I'll need to have two sets of
operations.

I doubt very much that this will work well.

How should I design such a dual-PHC device driver? Just register two
separate clocks, one for the timestamping counter, the other for the
scheduling/policing PTP clock, and have phc2sys keep them in sync
externally to the driver?

But how would phc2sys do this?  By comparing clock_gettime() values?
That would surely introduce unnecessary time error.

Or implement the hardware corrections
alongside the timecounter ones, and expose a single PHC (and for
clock_gettime, just pick one of the time sources)?

I would implement the hardware clock and drop the timecounter
altogether.

HTH,
Richard