Re: [PATCH 1/5] ptp: Added a brand new class driver for ptp clocks.

[Richard Cochran]

On Mon, Aug 16, 2010 at 09:59:39PM +0200, Arnd Bergmann wrote:
> Why does it matter how long it takes to read the clock? I wasn't thinking
> of replacing the system clock with this, just exposing the additional
> clock as a new clockid_t value that can be accessed using the existing
> syscalls.

Okay, now I see. You are suggesting this:

      clock_gettime(CLOCK_PTP, &ts);
      clock_settime(CLOCK_PTP, &ts);

I like this. If there is agreement about it, I am happy to implement
the PTP stuff that way.

> Why did you not want to add syscalls? Adding ioctls instead of syscalls
> does not make the interface better, just less visible.

I bet that, had I posted patch set with new syscalls, someone would
have said, "You are adding new syscalls. Can't you just use a char
device instead!"

If you add syscalls and introduce CLOCK_PTP, then you add it to
everyone's kernel, even those people who never heard of PTP. A char
device has the advantage that can it be simply ignored. Also, a
syscall has got to have the right form from the very beginning. If the
next generation of PTP hardware looks very different, then it is not
that much of a crime to change an ioctl interface, provided it has
versioning.

Richard

--
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to majordomo@xxxxxxxxxxxxxxx
More majordomo info at  http://vger.kernel.org/majordomo-info.html
Please read the FAQ at  http://www.tux.org/lkml/