From: Arnd Bergmann <arnd@arndb.de>
To: Richard Cochran <richardcochran@gmail.com>
Subject: Re: [PATCH 1/5] ptp: Added a brand new class driver for ptp clocks.
Date: Thu, 19 Aug 2010 14:29:49 +0200
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Cc: john stultz <johnstul@us.ibm.com>, linuxppc-dev@lists.ozlabs.org,
        Rodolfo Giometti <giometti@linux.it>, netdev@vger.kernel.org,
        devicetree-discuss@lists.ozlabs.org, linux-kernel@vger.kernel.org,
        linux-arm-kernel@lists.infradead.org, Krzysztof Halasa <khc@pm.waw.pl>
References: <cover.1281956490.git.richard.cochran@omicron.at> <201008181702.03384.arnd@arndb.de> <20100819092246.GA8484@riccoc20.at.omicron.at>
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On Thursday 19 August 2010, Richard Cochran wrote:
> 
> On Wed, Aug 18, 2010 at 05:02:03PM +0200, Arnd Bergmann wrote:
> > You might want to use callbacks for these system calls that you
> > can register to at module load time, like it is done for the
> > existing syscalls.
> 
> Can you point me to a specific example?

The struct k_clock contains callback functions to clock source
specific implementations of the syscalls and other functions.
Adding a new clock source that is (potentially) implemented
as a module means you have to define a new k_clock in that module
that you register using register_posix_clock.

If you need additional syscalls to be implemented by the same
module, you can put more callback functions into struct k_clock
that would then only be implemented by the new module.

> > The simpler way (e.g. for testing) is using Kconfig dependencies, like
> > 
> > config PTP
> >       bool "IEEE 1588 Precision Time Protocol"
> > 
> > config PPS
> >       tristate "Pulse per Second"
> >       depends on PTP || !PTP
> > 
> > The depends statement is a way of expressing that when PTP is enabled,
> > PPS cannot be a module, while it may be a module if PTP is disabled.
> 
> THis did not work for me.
> 
> What I got was, in effect, two independent booleans.

Hmm, right. I wonder what I was thinking of then.

You can certainly do

config PTP
	bool "IEEE 1588 Precision Time Protocol"
	depends on PPS != m

but that will hide the PTP option if PPS is set to 'm', which is normally
not what you want.

	Arnd
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