iio: adc: ad400x: Specify PWM parameters in nanoseconds

With ref_clk running with a rate not bigger than 1 GHz there is no gain
in using picosecond units as two different PWM settings differ by at
least one nanosecond. So there is no need to differ from upstream where
the pwm subsystem uses nanoseconds to specify PWM parameters.

With the goal to drop support for time_unit, don't explicitly set
cnv_state.time_unit = PWM_UNIT_NSEC but rely on this being the default.

Signed-off-by: Uwe Kleine-König <u.kleine-koenig@baylibre.com>

Author: ukleinek

drivers/iio/adc/ad400x.c

@@ -204,17 +204,16 @@ static int ad400x_get_sampling_freq(struct ad400x_state *st)
 
 static int __ad400x_set_sampling_freq(struct ad400x_state *st, int freq)
 {
-	unsigned long long ref_clk_period_ps;
+	unsigned long long ref_clk_period_ns;
 	struct pwm_state cnv_state;
 
 	/* Sync up PWM state and prepare for pwm_apply_state(). */
 	pwm_init_state(st->cnv_trigger, &cnv_state);
 
-	ref_clk_period_ps = DIV_ROUND_CLOSEST_ULL(1000000000000,
+	ref_clk_period_ns = DIV_ROUND_CLOSEST_ULL(NSEC_PER_SEC,
 						  st->ref_clk_rate);
-	cnv_state.period = DIV_ROUND_CLOSEST_ULL(1000000000000, freq);
-	cnv_state.duty_cycle = ref_clk_period_ps;
-	cnv_state.time_unit = PWM_UNIT_PSEC;
+	cnv_state.period = DIV_ROUND_CLOSEST_ULL(NSEC_PER_SEC, freq);
+	cnv_state.duty_cycle = ref_clk_period_ns;
 	return pwm_apply_state(st->cnv_trigger, &cnv_state);
 }