Re: [PATCH v2 2/4] clock: Add ClockPreUpdate callback event type

[Hao Wu <wuhaotsh@google.com>]

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On Tue, Feb 9, 2021 at 5:21 AM Peter Maydell <peter.maydell@linaro.org>
wrote:

> Add a new callback event type ClockPreUpdate, which is called on
> period changes before the period is updated.
>
> Signed-off-by: Peter Maydell <peter.maydell@linaro.org>
>
Reviewed-by: Hao Wu <wuhaotsh@google.com>

> ---
>  docs/devel/clocks.rst | 9 ++++++++-
>  include/hw/clock.h    | 1 +
>  hw/core/clock.c       | 3 +++
>  3 files changed, 12 insertions(+), 1 deletion(-)
>
> diff --git a/docs/devel/clocks.rst b/docs/devel/clocks.rst
> index cd344e3fe5d..f0391e76b4f 100644
> --- a/docs/devel/clocks.rst
> +++ b/docs/devel/clocks.rst
> @@ -181,7 +181,14 @@ events.
>
>  The events currently supported are:
>
> - * ``ClockUpdate`` : called after the input clock's period has changed
> + * ``ClockPreUpdate`` : called when the input clock's period is about to
> +   update. This is useful if the device needs to do some action for
> +   which it needs to know the old value of the clock period. During
> +   this callback, Clock API functions like ``clock_get()`` or
> +   ``clock_ticks_to_ns()`` will use the old period.
> + * ``ClockUpdate`` : called after the input clock's period has changed.
> +   During this callback, Clock API functions like ``clock_ticks_to_ns()``
> +   will use the new period.
>
>  Note that a clock only has one callback: it is not possible to register
>  different functions for different events. You must register a single
> diff --git a/include/hw/clock.h b/include/hw/clock.h
> index 5c73b4e7ae9..d7a6673c29e 100644
> --- a/include/hw/clock.h
> +++ b/include/hw/clock.h
> @@ -30,6 +30,7 @@ OBJECT_DECLARE_SIMPLE_TYPE(Clock, CLOCK)
>   */
>  typedef enum ClockEvent {
>      ClockUpdate = 1, /* Clock period has just updated */
> +    ClockPreUpdate = 2, /* Clock period is about to update */
>  } ClockEvent;
>
>  typedef void ClockCallback(void *opaque, ClockEvent event);
> diff --git a/hw/core/clock.c b/hw/core/clock.c
> index 71dc1f4de65..2c86091d8a3 100644
> --- a/hw/core/clock.c
> +++ b/hw/core/clock.c
> @@ -80,6 +80,9 @@ static void clock_propagate_period(Clock *clk, bool
> call_callbacks)
>
>      QLIST_FOREACH(child, &clk->children, sibling) {
>          if (child->period != clk->period) {
> +            if (call_callbacks) {
> +                clock_call_callback(child, ClockPreUpdate);
> +            }
>              child->period = clk->period;
>              trace_clock_update(CLOCK_PATH(child), CLOCK_PATH(clk),
>                                 CLOCK_PERIOD_TO_HZ(clk->period),
> --
> 2.20.1
>
>
>

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