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

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Message-Id: <201008271403.41949.arnd@arndb.de>
Date:	Fri, 27 Aug 2010 14:03:41 +0200
From:	Arnd Bergmann <arnd@...db.de>
To:	Richard Cochran <richardcochran@...il.com>
Cc:	john stultz <johnstul@...ibm.com>, netdev@...r.kernel.org,
	linux-kernel@...r.kernel.org, linuxppc-dev@...ts.ozlabs.org,
	devicetree-discuss@...ts.ozlabs.org,
	linux-arm-kernel@...ts.infradead.org,
	Krzysztof Halasa <khc@...waw.pl>,
	Rodolfo Giometti <giometti@...ux.it>
Subject: Re: [PATCH 1/5] ptp: Added a brand new class driver for ptp clocks.

On Friday 27 August 2010, Richard Cochran wrote:
> On Mon, Aug 23, 2010 at 01:21:39PM -0700, john stultz wrote:
> > On Thu, 2010-08-19 at 17:38 +0200, Richard Cochran wrote:
> > > On Thu, Aug 19, 2010 at 02:28:04PM +0200, Arnd Bergmann wrote:
> > > > Have you considered passing a struct timex instead of ppb and ts?
> > > 
> > > Yes, but the timex is not suitable, IMHO.
> > 
> > Could you expand on this?
> 
> We need to able to specify that the call is for a PTP clock. We could
> add that to the modes flag, like this:
> 
> /*timex.h*/
> #define ADJ_PTP_0 0x10000
> #define ADJ_PTP_1 0x20000
> #define ADJ_PTP_2 0x30000
> #define ADJ_PTP_3 0x40000
>
> I can live with this, if everyone else can, too.

My suggestion was actually to have a new syscall with the existing
structure, and pass a clockid_t value to it, similar to your
sys_clock_adjtime(), not change the actual sys_adjtime syscall.
  
> > Could we not add a adjustment mode ADJ_SETOFFSET or something that would
> > provide the instantaneous offset correction?
> 
> Yes, but we would also need to add a struct timespec to the struct
> timex, in order to get nanosecond resolution. I think it would be
> possible to do in the padding at the end?

Yes, that's exactly what the padding is for. Instead of timespec, you can
probably have a extra values for replacing the existing ppm values with
ppb values.

	Arnd
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