On Mon, Aug 16, 2010 at 04:26:23PM +0200, Arnd Bergmann wrote:

Have you considered integrating the subsystem into the Posix clock/timer
framework?

Yes, but see below.
 

I can't really tell from reading the source if this is possible or
not, but my feeling is that if it can be done, that would be a much
nicer interface. We already have clock_gettime/clock_settime/
timer_settime/... system calls, and while you'd need to add another
clockid and some syscalls, my feeling is that it will be more
usable in the end.

You are not the first person to ask about this. See this link for
longer explanation of why I did not go that way:

  http://marc.info/?l=linux-netdev&m=127669810232201&w=2

You *could* offer the PTP clock as a Linux clock source/event device,
and I agree that it would be nicer. However, the problem is, what do
you do with the PHY based clocks?  Just one 16 bit read from a PHY
clock can take 40 usec, and you need four such read operations just to
get the current time value.

Also, I really did not want to add or change any syscalls. I could not
see a practical way to extend the existing syscalls to accommodate PTP
clocks.

Richard