iio: adc: ad4630: 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
state.time_unit = PWM_UNIT_NSEC but rely on this being the default.

Note that in corner cases this change might result in different settings
being used. However with the current implemention in the axi-pwmgen
driver the result only gets more exact because only one rounding
operation is done.

Note further the rounding of the phase value isn't exact. I didn't try
to do the math to make this exact because I assume having .phase >
.period doesn't have the intended effect anyhow. Also with an input rate
of less than 500 MHz for the PWM the error cancels out when the absolute
time is converted to clock ticks.

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

Author: ukleinek

drivers/iio/adc/ad4630.c

@@ -370,17 +370,15 @@ static int ad4630_read_avail(struct iio_dev *indio_dev,
 static int __ad4630_set_sampling_freq(const struct ad4630_state *st, unsigned int freq)
 {
 	struct pwm_state conv_state = {
-		.duty_cycle = 10000,
-		.time_unit = PWM_UNIT_PSEC,
+		.duty_cycle = 10,
 		.enabled = true,
 	}, fetch_state = {
-		.duty_cycle = 10000,
-		.time_unit = PWM_UNIT_PSEC,
+		.duty_cycle = 10,
 		.enabled = true,
 	};
 	int ret;
 
-	conv_state.period =  DIV_ROUND_CLOSEST_ULL(PICO, freq);
+	conv_state.period = DIV_ROUND_CLOSEST(NSEC_PER_SEC, freq);
 	ret = pwm_apply_state(st->conv_trigger, &conv_state);
 	if (ret)
 		return ret;
@@ -406,7 +404,7 @@ static int __ad4630_set_sampling_freq(const struct ad4630_state *st, unsigned in
 	 * tsync + tquiet_con_delay being tsync the conversion signal period
 	 * and tquiet_con_delay 9.8ns. Hence set the PWM phase accordingly.
 	 */
-	fetch_state.phase = fetch_state.period + 9800;
+	fetch_state.phase = fetch_state.period + 10;
 
 	return pwm_apply_state(st->fetch_trigger, &fetch_state);
 }