iio: multiplexer: iio-mux: Support settle-time-us property

If the devicetree specifies that the hardware requires a settle time,
pass this time on to the mux APIs.

Signed-off-by: Vincent Whitchurch <[e-mail]>
Reviewed-by: Lars-Peter Clausen <[e-mail]>
Tested-by: Lars-Peter Clausen <[e-mail]>
Acked-by: Peter Rosin <[e-mail]>
Link: https://lore.kernel.org/r/[e-mail]
Signed-off-by: Jonathan Cameron <[e-mail]>

drivers/iio/multiplexer/iio-mux.c

···
 	struct iio_chan_spec *chan;
 	struct iio_chan_spec_ext_info *ext_info;
 	struct mux_child *child;
+	u32 delay_us;
 };
 
 static int iio_mux_select(struct mux *mux, int idx)
···
 	int ret;
 	int i;
 
-	ret = mux_control_select(mux->control, chan->channel);
+	ret = mux_control_select_delay(mux->control, chan->channel,
+				       mux->delay_us);
 	if (ret < 0) {
 		mux->cached_state = -1;
 		return ret;
···
 
 	mux->parent = parent;
 	mux->cached_state = -1;
+
+	mux->delay_us = 0;
+	of_property_read_u32(np, "settle-time-us", &mux->delay_us);
 
 	indio_dev->name = dev_name(dev);
 	indio_dev->info = &mux_info;