iio:core: timestamping clock selection support

Adds a new per-device sysfs attribute "current_timestamp_clock" to allow
userspace to select a particular POSIX clock for buffered samples and
events timestamping.

Following clocks, as listed in clock_gettime(2), are supported:
CLOCK_REALTIME, CLOCK_MONOTONIC, CLOCK_MONOTONIC_RAW,
CLOCK_REALTIME_COARSE, CLOCK_MONOTONIC_COARSE, CLOCK_BOOTTIME and
CLOCK_TAI.

Signed-off-by: Gregor Boirie <gregor.boirie@parrot.com>
Acked-by: Sanchayan Maity <maitysanchayan@gmail.com>
Signed-off-by: Jonathan Cameron <jic23@kernel.org>
diff --git a/drivers/iio/adc/max1363.c b/drivers/iio/adc/max1363.c
index 998dc3c..73af306 100644
--- a/drivers/iio/adc/max1363.c
+++ b/drivers/iio/adc/max1363.c
@@ -788,7 +788,7 @@
 {
 	struct iio_dev *indio_dev = private;
 	struct max1363_state *st = iio_priv(indio_dev);
-	s64 timestamp = iio_get_time_ns();
+	s64 timestamp = iio_get_time_ns(indio_dev);
 	unsigned long mask, loc;
 	u8 rx;
 	u8 tx[2] = { st->setupbyte,
@@ -1506,7 +1506,8 @@
 	if (b_sent < 0)
 		goto done_free;
 
-	iio_push_to_buffers_with_timestamp(indio_dev, rxbuf, iio_get_time_ns());
+	iio_push_to_buffers_with_timestamp(indio_dev, rxbuf,
+					   iio_get_time_ns(indio_dev));
 
 done_free:
 	kfree(rxbuf);