iio: hrtimer-trigger: Mark hrtimer to expire in hard interrupt context

[ Upstream commit 0178297 ]

On PREEMPT_RT enabled kernels unmarked hrtimers are moved into soft
interrupt expiry mode by default.

The IIO hrtimer-trigger needs to run in hard interrupt context since it
will end up calling generic_handle_irq() which has the requirement to run
in hard interrupt context.

Explicitly specify that the timer needs to run in hard interrupt context by
using the HRTIMER_MODE_REL_HARD flag.

Fixes: f5c2f02 ("hrtimer: Move unmarked hrtimers to soft interrupt expiry on RT")
Reported-by: Christian Eggers <ceggers@arri.de>
Signed-off-by: Lars-Peter Clausen <lars@metafoo.de>
Acked-by: Sebastian Andrzej Siewior <bigeasy@linutronix.de>
Link: https://lore.kernel.org/r/20201117103751.16131-1-lars@metafoo.de
Signed-off-by: Jonathan Cameron <Jonathan.Cameron@huawei.com>
Signed-off-by: Sasha Levin <sashal@kernel.org>

drivers/iio/trigger/iio-trig-hrtimer.c

@@ -102,7 +102,7 @@ static int iio_trig_hrtimer_set_state(struct iio_trigger *trig, bool state)
 
 	if (state)
 		hrtimer_start(&trig_info->timer, trig_info->period,
-			      HRTIMER_MODE_REL);
+			      HRTIMER_MODE_REL_HARD);
 	else
 		hrtimer_cancel(&trig_info->timer);
 
@@ -132,7 +132,7 @@ static struct iio_sw_trigger *iio_trig_hrtimer_probe(const char *name)
 	trig_info->swt.trigger->ops = &iio_hrtimer_trigger_ops;
 	trig_info->swt.trigger->dev.groups = iio_hrtimer_attr_groups;
 
-	hrtimer_init(&trig_info->timer, CLOCK_MONOTONIC, HRTIMER_MODE_REL);
+	hrtimer_init(&trig_info->timer, CLOCK_MONOTONIC, HRTIMER_MODE_REL_HARD);
 	trig_info->timer.function = iio_hrtimer_trig_handler;
 
 	trig_info->sampling_frequency = HRTIMER_DEFAULT_SAMPLING_FREQUENCY;