Re: [PATCH v2 5/9] clocksource/cadence_ttc: Adjust interval in clocknotifier

[Daniel Lezcano]

On 11/27/2013 02:04 AM, Soren Brinkmann wrote:
> The clockevent has to be reprogrammed if the timer's input
> clock frequency changes and the timer is in periodic mode, in order to
> maintain the correct timer interval.
>
> Signed-off-by: Soren Brinkmann <soren.brinkmann@xxxxxxxxxx>
> ---
> v2:
>   - adjust the timer interval while the timer interrupt is disabled
> ---
>   drivers/clocksource/cadence_ttc_timer.c | 12 +++++++++---
>   1 file changed, 9 insertions(+), 3 deletions(-)
>
> diff --git a/drivers/clocksource/cadence_ttc_timer.c b/drivers/clocksource/cadence_ttc_timer.c
> index 246d018d1e63..77517675653e 100644
> --- a/drivers/clocksource/cadence_ttc_timer.c
> +++ b/drivers/clocksource/cadence_ttc_timer.c
> @@ -322,6 +322,9 @@ static int ttc_rate_change_clockevent_cb(struct notifier_block *nb,
>   	switch (event) {
>   	case POST_RATE_CHANGE:
>   	{
> +		/* update cached frequency */
> +		ttc->freq = ndata->new_rate;
> +
>   		/*
>   		 * clockevents_update_freq should be called with IRQ disabled on
>   		 * the CPU the timer provides events for. The timer we use is
> @@ -329,12 +332,15 @@ static int ttc_rate_change_clockevent_cb(struct notifier_block *nb,
>   		 * cores.
>   		 */
>   		disable_irq(ttcce->ce.irq);
> +
>   		clockevents_update_freq(&ttcce->ce,
>   				ndata->new_rate / PRESCALE);
> -		enable_irq(ttcce->ce.irq);
>
> -		/* update cached frequency */
> -		ttc->freq = ndata->new_rate;
> +		if (ttcce->ce.mode == CLOCK_EVT_MODE_PERIODIC)
> +			ttc_set_interval(ttc, DIV_ROUND_CLOSEST(ttc->freq,
> +						PRESCALE * HZ));
> +
> +		enable_irq(ttcce->ce.irq);
>
>   		/* fall through */
>   	}

When looking at the smp_twd.c, there is a similar need.

There are a couple of notifier used on for cpufreq and one for clock 
rate change.

Wouldn't make sense to add the notifier calls and registration in the 
time framework and add the callbacks in the dev ops ? The switch would 
be in the timer framework and perhaps the irq disabling may be easier to 
deal with ?

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