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


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