From: Arnd Bergmann <arnd@arndb•de>
To: Richard Cochran <richardcochran@gmail•com>
Cc: john stultz <johnstul@us•ibm.com>,
netdev@vger•kernel.org, linux-kernel@vger•kernel.org,
linuxppc-dev@lists•ozlabs.org,
devicetree-discuss@lists•ozlabs.org,
linux-arm-kernel@lists•infradead.org,
Krzysztof Halasa <khc@pm•waw.pl>,
Rodolfo Giometti <giometti@linux•it>
Subject: Re: [PATCH 1/5] ptp: Added a brand new class driver for ptp clocks.
Date: Thu, 19 Aug 2010 14:28:04 +0200 [thread overview]
Message-ID: <201008191428.04546.arnd@arndb.de> (raw)
In-Reply-To: <20100819055518.GA4084@riccoc20.at.omicron.at>
On Thursday 19 August 2010, Richard Cochran wrote:
> On Wed, Aug 18, 2010 at 05:12:56PM -0700, john stultz wrote:
> > On Wed, 2010-08-18 at 09:19 +0200, Richard Cochran wrote:
> > > The timer/alarm stuff is "ancillary" and is not at all necessary. It
> > > is just a "nice to have." I will happily remove it, if it is too
> > > troubling for people.
> >
> > If there's a compelling argument for it, I'm interested to hear. But
> > again, it seems like just
> > yet-another-way-to-get-alarm/timer-functionality, so before we add an
> > extra API (or widen an existing API) I'd like to understand the need.
>
> We don't really need it, IMHO.
>
> But if we offer clockid_t CLOCK_PTP, then we get timer_settime()
> without any extra effort.
Makes sense.
> > So in thinking about this, try to focus on what the new clock_id
> > provides that the other existing clockids do not? Are they at comparable
> > levels of abstraction? 15 years from now, are folks likely to still be
> > using it? Will it be maintainable? etc...
>
> Arnd convinced me that clockid_t=CLOCK_PTP is a good fit.
My point was that a syscall is better than an ioctl based interface here,
which I definitely still think. Given that John knows much more about
clocks than I do, we still need to get agreement on the question that
he raised, which is whether we actually need to expose this clock to the
user or not.
If we can find a way to sync system time accurate enough with PTP and
PPS, user applications may not need to see two separate clocks at all.
> My plan would be to introduce just one additional syscall:
>
> SYSCALL_DEFINE3(clock_adjtime, const clockid_t, clkid,
> int, ppb, struct timespec __user *, ts)
>
> ppb - desired frequency adjustment in parts per billion
> ts - desired time step (or jump) in <sec,nsec> to correct
> a measured offset
>
> Arguably, this syscall might be useful for other clocks, too.
This is a mix of adjtime and adjtimex with the addition of
the clkid parameter, right?
Have you considered passing a struct timex instead of ppb and ts?
Is using ppb instead of the timex ppm required to get the accuracy
you want?
Arnd
next prev parent reply other threads:[~2010-08-19 12:27 UTC|newest]
Thread overview: 56+ messages / expand[flat|nested] mbox.gz Atom feed top
2010-08-16 11:17 [PATCH v5 0/5] ptp: IEEE 1588 clock support Richard Cochran
2010-08-16 11:17 ` [PATCH 1/5] ptp: Added a brand new class driver for ptp clocks Richard Cochran
[not found] ` <363bd749a38d0b785d8431e591bf54c38db4c2d7.1281956490.git.richard.cochran-3mrvs1K0uXizZXS1Dc/lvw@public.gmane.org>
2010-08-16 14:26 ` Arnd Bergmann
2010-08-16 19:00 ` Richard Cochran
2010-08-16 19:59 ` Arnd Bergmann
2010-08-17 8:32 ` Richard Cochran
2010-08-17 9:25 ` Arnd Bergmann
[not found] ` <201008170925.55592.arnd-r2nGTMty4D4@public.gmane.org>
2010-08-17 10:52 ` Richard Cochran
[not found] ` <20100817105232.GA9079-7KxsofuKt4IfAd9E5cN8NEzG7cXyKsk/@public.gmane.org>
2010-08-17 11:36 ` Arnd Bergmann
2010-08-18 0:40 ` john stultz
[not found] ` <201008171336.29375.arnd-r2nGTMty4D4@public.gmane.org>
2010-08-18 14:04 ` Richard Cochran
2010-08-18 15:02 ` Arnd Bergmann
[not found] ` <201008181702.03384.arnd-r2nGTMty4D4@public.gmane.org>
2010-08-19 9:22 ` Richard Cochran
2010-08-19 12:29 ` Arnd Bergmann
2010-08-19 15:23 ` Ira W. Snyder
2010-08-19 15:48 ` Arnd Bergmann
2010-08-16 19:24 ` john stultz
2010-08-16 19:38 ` john stultz
[not found] ` <AANLkTik_2MKMhOuDGOmu8Kzyq-ipLe+Bxrb3FaD+Tv4U-JsoAwUIsXosN+BqQ9rBEUg@public.gmane.org>
2010-08-17 8:53 ` Richard Cochran
2010-08-18 0:22 ` john stultz
2010-08-18 7:19 ` Richard Cochran
2010-08-19 0:12 ` john stultz
[not found] ` <1282176776.2865.100.camel-bi+AKbBUZKY6gyzm1THtWbp2dZbC/Bob@public.gmane.org>
2010-08-19 5:55 ` Richard Cochran
2010-08-19 12:28 ` Arnd Bergmann [this message]
2010-08-19 15:38 ` Richard Cochran
2010-08-23 20:21 ` john stultz
[not found] ` <1282594899.3111.358.camel-bi+AKbBUZKY6gyzm1THtWbp2dZbC/Bob@public.gmane.org>
2010-08-27 11:08 ` Richard Cochran
[not found] ` <20100827110855.GA11657-7KxsofuKt4IfAd9E5cN8NEzG7cXyKsk/@public.gmane.org>
2010-08-27 12:03 ` Arnd Bergmann
2010-08-27 20:56 ` John Stultz
2010-08-27 12:45 ` Alan Cox
2010-08-27 20:14 ` John Stultz
2010-08-23 20:08 ` john stultz
2010-08-24 18:30 ` Stephan Gatzka
2010-08-25 9:40 ` Christian Riesch
2010-08-27 1:57 ` john stultz
[not found] ` <1282874269.4371.74.camel-bi+AKbBUZKY6gyzm1THtWbp2dZbC/Bob@public.gmane.org>
2010-08-27 7:57 ` Richard Cochran
2010-08-27 12:41 ` Alan Cox
[not found] ` <20100827134154.50eef56c-qBU/x9rampVanCEyBjwyrvXRex20P6io@public.gmane.org>
2010-08-27 14:02 ` Richard Cochran
[not found] ` <20100827140205.GA3293-7KxsofuKt4IfAd9E5cN8NEzG7cXyKsk/@public.gmane.org>
2010-08-27 14:50 ` Alan Cox
2010-08-27 15:35 ` M. Warner Losh
2010-08-29 13:32 ` Christian Riesch
[not found] ` <1282594125.3111.344.camel-bi+AKbBUZKY6gyzm1THtWbp2dZbC/Bob@public.gmane.org>
2010-08-27 12:38 ` Richard Cochran
[not found] ` <20100827123849.GC11657-7KxsofuKt4IfAd9E5cN8NEzG7cXyKsk/@public.gmane.org>
2010-08-27 13:38 ` Alan Cox
[not found] ` <20100827143844.646eccf6-qBU/x9rampVanCEyBjwyrvXRex20P6io@public.gmane.org>
2010-08-27 14:34 ` Richard Cochran
[not found] ` <20100827143437.GB3293-7KxsofuKt4IfAd9E5cN8NEzG7cXyKsk/@public.gmane.org>
2010-08-27 15:06 ` Alan Cox
2010-08-27 15:21 ` Patrick Loschmidt
2010-08-27 16:17 ` Jacob Keller
2010-08-27 22:30 ` John Stultz
2010-09-06 6:33 ` Richard Cochran
[not found] ` <20100906063327.GA4549-7KxsofuKt4IfAd9E5cN8NEzG7cXyKsk/@public.gmane.org>
2010-09-21 16:54 ` Stephan Gatzka
2010-09-21 20:47 ` Kyle Moffett
[not found] ` <AANLkTinRM3_kBc5S3wV=_S6P8+x7A43kz0qSYbixJYnq-JsoAwUIsXosN+BqQ9rBEUg@public.gmane.org>
2010-09-22 10:14 ` Richard Cochran
2010-08-16 11:18 ` [PATCH 2/5] ptp: Added a clock that uses the Linux system time Richard Cochran
2010-08-16 11:18 ` [PATCH 3/5] ptp: Added a clock that uses the eTSEC found on the MPC85xx Richard Cochran
2010-08-16 11:18 ` [PATCH 4/5] ptp: Added a clock driver for the IXP46x Richard Cochran
2010-08-16 11:19 ` [PATCH 5/5] ptp: Added a clock driver for the National Semiconductor PHYTER Richard Cochran
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