The Clock framework allows users to specify a callback which is
called after the clock's period has been updated. Some users need to
also have a callback which is called before the clock period is
updated.
As the first step in adding support for notifying Clock users on
pre-update events, add an argument to the ClockCallback to specify
what event is being notified, and add an argument to the various
functions for registering a callback to specify which events are
of interest to that callback.
Note that the documentation update renders correct the previously
incorrect claim in 'Adding a new clock' that callbacks "will be
explained in a following section".
Signed-off-by: Peter Maydell<peter.maydell@linaro.org>
Reviewed-by: Philippe Mathieu-Daudé<f4bug@amsat.org>
Reviewed-by: Luc Michel<luc@lmichel.fr>
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