From: Richard Cochran <richardcochran@gmail.com>
To: "Christopher S. Hall" <christopher.s.hall@intel.com>
Cc: netdev@vger.kernel.org, linux-kernel@vger.kernel.org,
tglx@linutronix.de, hpa@zytor.com, mingo@redhat.com,
x86@kernel.org, jacob.e.keller@intel.com, davem@davemloft.net,
sean.v.kelley@intel.com
Subject: Re: [Intel PMC TGPIO Driver 0/5] Add support for Intel PMC Time GPIO Driver with PHC interface changes to support additional H/W Features
Date: Tue, 25 Feb 2020 18:47:07 -0800 [thread overview]
Message-ID: <20200226024707.GA10271@localhost> (raw)
In-Reply-To: <20200225233707.GA32079@skl-build>
On Tue, Feb 25, 2020 at 03:37:07PM -0800, Christopher S. Hall wrote:
> On Sun, Feb 02, 2020 at 08:08:38PM -0800, Richard Cochran wrote:
> > The TGPIO input clock, the ART, is a free running counter, but you
> > want to support frequency adjustments. Use a timecounter cyclecounter
> > pair.
>
> I'm concerned about the complexity that the timecounter adds to
> the driver. Specifically, the complexity of dealing with any rate mismatches
> between the timecounter and the periodic output signal. The phase
> error between the output and timecounter needs to be zero.
If I understood correctly, the device's outputs are generated from a
non-adjustable counter. So, no matter what, you will have the problem
of changing the pulse period in concert with the user changing the
desired frequency.
> My counter-proposal would be to use the real-time clock as the basis of the
> device clock. This is fairly simple because the relation between ART and the
> realtime clock is known. When output is enabled any phase error between
> the realtime clock and the periodic output signal is accumulated in the
> SYS_OFFSET result.
I don't understand how you intend to do this...
> This leaves the PHC API behavior as it is currently and uses the frequency
> adjust API to adjust the output rate.
>
> > Let the user dial a periodic output signal in the normal way.
> >
> > Let the user change the frequency in the normal way, and during this
> > call, adjust the counter values accordingly.
>
> Yes to both of the above.
So, why then do you need this?
+#define PTP_EVENT_COUNT_TSTAMP2 \
+ _IOWR(PTP_CLK_MAGIC, 19, struct ptp_event_count_tstamp)
If you can make the device work with the existing user space API,
ioctl(fd, PTP_PEROUT_REQUEST2, ...);
while (1) {
clock_adjtimex(FD_TO_CLOCKID(fd), ...);
}
that would be ideal. But I will push back on anything like the
following.
ioctl(fd, PTP_PEROUT_REQUEST2, ...);
while (1) {
clock_adjtimex(FD_TO_CLOCKID(fd), ...);
ioctl(fd, PTP_EVENT_COUNT_TSTAMP, ...);
}
But maybe I misunderstood?
Thanks,
Richard
next prev parent reply other threads:[~2020-02-26 2:47 UTC|newest]
Thread overview: 36+ messages / expand[flat|nested] mbox.gz Atom feed top
2019-12-11 21:48 [Intel PMC TGPIO Driver 0/5] Add support for Intel PMC Time GPIO Driver with PHC interface changes to support additional H/W Features christopher.s.hall
2019-12-11 21:48 ` [Intel PMC TGPIO Driver 1/5] drivers/ptp: Add Enhanced handling of reserve fields christopher.s.hall
2020-01-31 16:54 ` Jacob Keller
2020-02-03 1:45 ` Richard Cochran
2020-02-24 23:29 ` Christopher S. Hall
2020-01-31 17:02 ` Jacob Keller
2020-02-03 1:27 ` Richard Cochran
2020-02-24 23:23 ` Christopher S. Hall
2019-12-11 21:48 ` [Intel PMC TGPIO Driver 2/5] drivers/ptp: Add PEROUT2 ioctl frequency adjustment interface christopher.s.hall
2020-02-03 2:14 ` Richard Cochran
2020-02-26 0:20 ` Christopher S. Hall
2019-12-11 21:48 ` [Intel PMC TGPIO Driver 3/5] drivers/ptp: Add user-space input polling interface christopher.s.hall
2020-02-03 2:28 ` Richard Cochran
2019-12-11 21:48 ` [Intel PMC TGPIO Driver 4/5] x86/tsc: Add TSC support functions to support ART driven Time-Aware GPIO christopher.s.hall
2019-12-11 21:48 ` [Intel PMC TGPIO Driver 5/5] drivers/ptp: Add PMC Time-Aware GPIO Driver christopher.s.hall
2020-02-03 2:31 ` Richard Cochran
2020-02-07 17:10 ` Linus Walleij
2020-02-07 17:28 ` Andrew Lunn
2020-02-07 19:49 ` Andy Shevchenko
2020-02-07 19:52 ` Andy Shevchenko
2020-02-24 23:17 ` Christopher S. Hall
2020-01-31 15:08 ` [Intel PMC TGPIO Driver 0/5] Add support for Intel PMC Time GPIO Driver with PHC interface changes to support additional H/W Features Jakub Kicinski
2020-01-31 18:14 ` Thomas Gleixner
2020-02-24 22:40 ` Christopher S. Hall
2020-02-26 23:06 ` Thomas Gleixner
2020-03-03 1:56 ` Christopher S. Hall
2020-03-03 13:00 ` Linus Walleij
2020-03-03 15:23 ` Richard Cochran
2020-03-03 15:24 ` Thomas Gleixner
2020-03-08 19:14 ` Jonathan Cameron
2020-02-03 4:08 ` Richard Cochran
2020-02-03 18:27 ` Jacob Keller
2020-02-25 23:37 ` Christopher S. Hall
2020-02-26 2:47 ` Richard Cochran [this message]
2020-03-03 2:01 ` Christopher S. Hall
2020-02-07 17:17 ` Linus Walleij
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