iio: adc: adi-axi-adc: add axi_adc_oversampling_ratio_set

Add support for setting decimation rate.

Reviewed-by: David Lechner <dlechner@baylibre.com>
Reviewed-by: Nuno Sá <nuno.sa@analog.com>
Signed-off-by: Pop Ioan Daniel <pop.ioan-daniel@analog.com>
Link: https://patch.msgid.link/20250605150948.3091827-4-pop.ioan-daniel@analog.com
Signed-off-by: Jonathan Cameron <Jonathan.Cameron@huawei.com>

Author: PIoandan

drivers/iio/adc/adi-axi-adc.c

@@ -86,6 +86,9 @@
 #define ADI_AXI_ADC_REG_CHAN_CTRL_3(c)		(0x0418 + (c) * 0x40)
 #define   ADI_AXI_ADC_CHAN_PN_SEL_MASK		GENMASK(19, 16)
 
+#define ADI_AXI_ADC_REG_CHAN_USR_CTRL_2(c)	(0x0424 + (c) * 0x40)
+#define   ADI_AXI_ADC_CHAN_USR_CTRL_2_DEC_RATE_N_MASK		GENMASK(15, 0)
+
 /* IO Delays */
 #define ADI_AXI_ADC_REG_DELAY(l)		(0x0800 + (l) * 0x4)
 #define   AXI_ADC_DELAY_CTRL_MASK		GENMASK(4, 0)
@@ -248,6 +251,19 @@ static int axi_adc_test_pattern_set(struct iio_backend *back,
 	}
 }
 
+static int axi_adc_oversampling_ratio_set(struct iio_backend *back,
+					  unsigned int chan,
+					  unsigned int rate)
+{
+	struct adi_axi_adc_state *st = iio_backend_get_priv(back);
+
+	return regmap_update_bits(st->regmap,
+				  ADI_AXI_ADC_REG_CHAN_USR_CTRL_2(chan),
+				  ADI_AXI_ADC_CHAN_USR_CTRL_2_DEC_RATE_N_MASK,
+				  FIELD_PREP(ADI_AXI_ADC_CHAN_USR_CTRL_2_DEC_RATE_N_MASK,
+					     rate));
+}
+
 static int axi_adc_read_chan_status(struct adi_axi_adc_state *st, unsigned int chan,
 				    unsigned int *status)
 {
@@ -600,6 +616,7 @@ static const struct iio_backend_ops adi_axi_adc_ops = {
 	.test_pattern_set = axi_adc_test_pattern_set,
 	.chan_status = axi_adc_chan_status,
 	.interface_type_get = axi_adc_interface_type_get,
+	.oversampling_ratio_set = axi_adc_oversampling_ratio_set,
 	.debugfs_reg_access = iio_backend_debugfs_ptr(axi_adc_reg_access),
 	.debugfs_print_chan_status = iio_backend_debugfs_ptr(axi_adc_debugfs_print_chan_status),
 };