Hi Daniel,
On Thu, Dec 12, 2013 at 01:15:38PM +0100, Daniel Lezcano wrote:
> 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.
Right, but with my proposed patches a call to clockevents_update_freq()
should be all that is needed.
>
> There are a couple of notifier used on for cpufreq and one for clock
> rate change.
Only one is actually used I think, depending on what kernel
infrastructure is available.
>
> 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 ?
I don't think that works - at least not that easy - because timers could
have all different input clocks. The twd is kind of special since it always
uses the CPU clock. And - unfortunately - our TTC implementation on Zynq
does it similar. But that is not the generic case and I don't know if it
makes sense/is possible to handle this in the timer core. It would mean the
timer core would need to keep track of the timers + their input clocks.
I was hoping that Zynq, twd and arm_global_timer are rather the
exception and that the majority of timer HW is provided a fixed and stable
input frequency - as the arm generic timer spec demands.
Sören
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