iio: adc: at91-sama5d2_adc: adjust osr based on specific platform data

ADC captures data on 12 bits (if oversampling is not enabled). When using
oversampling captured data could go up to 14 bits for SAMA5D2 or up to
16 bits for SAMA7G5 (depending on oversampling settings). All the channels
that are subject of oversampling are registered as 14 or 16 real bits.
Depending on the oversampling settings the ADC converted value need to be
shifted up to 14 or 16 to cope with realbits value registered to IIO
subsystem. Commit adds platform specific information to know if we
run on a system with up to 14 or 16 bits ADC converted data.
Signed-off-by: Claudiu Beznea <claudiu.beznea@microchip.com>
Link: https://lore.kernel.org/r/20220803102855.2191070-11-claudiu.beznea@microchip.comSigned-off-by: Jonathan Cameron <Jonathan.Cameron@huawei.com>

drivers/iio/adc/at91-sama5d2_adc.c

@@ -408,6 +408,7 @@ static const struct at91_adc_reg_layout sama7g5_layout = {
  * @osr_mask:		oversampling ratio bitmask on EMR register
  * @oversampling_avail:	available oversampling values
  * @oversampling_avail_no: number of available oversampling values
+ * @chan_realbits:	realbits for registered channels
  */
 struct at91_adc_platform {
 	const struct at91_adc_reg_layout	*layout;
@@ -422,6 +423,7 @@ struct at91_adc_platform {
 	unsigned int				osr_mask;
 	unsigned int				oversampling_avail[3];
 	unsigned int				oversampling_avail_no;
+	unsigned int				chan_realbits;
 };
 
 /**
@@ -623,6 +625,7 @@ static const struct at91_adc_platform sama5d2_platform = {
 	.osr_mask = GENMASK(17, 16),
 	.oversampling_avail = { 1, 4, 16, },
 	.oversampling_avail_no = 3,
+	.chan_realbits = 14,
 };
 
 static const struct at91_adc_platform sama7g5_platform = {
@@ -641,6 +644,7 @@ static const struct at91_adc_platform sama7g5_platform = {
 	.osr_mask = GENMASK(18, 16),
 	.oversampling_avail = { 1, 4, 16, },
 	.oversampling_avail_no = 3,
+	.chan_realbits = 16,
 };
 
 static int at91_adc_chan_xlate(struct iio_dev *indio_dev, int chan)
@@ -777,19 +781,24 @@ static int at91_adc_config_emr(struct at91_adc_state *st,
 
 static int at91_adc_adjust_val_osr(struct at91_adc_state *st, int *val)
 {
-	if (st->oversampling_ratio == 1) {
-		/*
-		 * in this case we only have 12 bits of real data, but channel
-		 * is registered as 14 bits, so shift left two bits
-		 */
-		*val <<= 2;
-	} else if (st->oversampling_ratio == 4) {
+	int nbits, diff;
+
+	if (st->oversampling_ratio == 1)
+		nbits = 12;
+	else if (st->oversampling_ratio == 4)
+		nbits = 13;
+	else if (st->oversampling_ratio == 16)
+		nbits = 14;
+	else
+		/* Should not happen. */
+		return -EINVAL;
+
 	/*
-		 * in this case we have 13 bits of real data, but channel
-		 * is registered as 14 bits, so left shift one bit
+	 * We have nbits of real data and channel is registered as
+	 * st->soc_info.platform->chan_realbits, so shift left diff bits.
 	 */
-		*val <<= 1;
-	}
+	diff = st->soc_info.platform->chan_realbits - nbits;
+	*val <<= diff;
 
 	return IIO_VAL_INT;
 }