Hi Daniel,
On Tue, Nov 12, 2013 at 05:29:45PM +0100, Daniel Lezcano wrote:
> On 11/08/2013 10:21 PM, 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 <[email protected]>
> >---
> > drivers/clocksource/cadence_ttc_timer.c | 4 ++++
> > 1 file changed, 4 insertions(+)
> >
> >diff --git a/drivers/clocksource/cadence_ttc_timer.c
> >b/drivers/clocksource/cadence_ttc_timer.c
> >index a92350b55d32..68a336038d8f 100644
> >--- a/drivers/clocksource/cadence_ttc_timer.c
> >+++ b/drivers/clocksource/cadence_ttc_timer.c
> >@@ -338,6 +338,10 @@ static int ttc_rate_change_clockevent_cb(struct
> >notifier_block *nb,
> > /* 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));
> >+
>
> Couldn't be racy ?
I guess you're right. What would be the proper way to resolve it? If we
look at a little more code things look like this:
local_irq_save(flags);
clockevents_update_freq(&ttcce->ce,
ndata->new_rate / PRESCALE);
local_irq_restore(flags);
/* 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));
Would it be enough to move the ttc_set_interval() call within the
section where local IRQs are disabled? I have the feeling for this timer
the local_irq_save() may in general not be the right option since the
timer is not CPU local.
Should we probably change this do irq_disable(ttcce->ce.irq)?
Thanks,
Sören
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