[PATCH] iio: adc: rockchip_saradc: Add support for RV1106

[Vladislav Leonov]

The Successive Approximation ADC (SARADC) in RV1106 uses the v2
controller and supports:
- 10-bit resolution
- Up to 1MS/s sampling rate
- 2 single-ended input channels

"dt-bindings: iio: adc: rockchip-saradc: Add RV1106 compatible"
documents "rockchip,rv1106-saradc" as falling back to
"rockchip,rk3588-saradc" (see Link below). The two IP blocks are not
equivalent, though: per the RV1106 TRM v0.3, chapter 20 (SAR-ADC),
RV1106 only has 2 channels at 10-bit resolution, versus 8 channels
at 12-bit on RK3588. Without a dedicated match entry, the driver
binds via the fallback compatible and uses the RK3588 channel table,
which reports 8 channels instead of 2, and an in_voltage_scale that
is off by exactly 4x (4096 vs 1024 full-scale).

Add a dedicated compatible/data pair for RV1106 with the correct
2-channel, 10-bit layout.

Tested on a custom RV1106-based board, with:

  &saradc {
	vref-supply = <&vcc_saradc>; /* 1.8V fixed regulator */
	status = "okay";
  };

Before this patch:
  # ls /sys/bus/iio/devices/iio:device0/in_voltage*_raw | wc -l
  8
  # cat /sys/bus/iio/devices/iio:device0/in_voltage_scale
  0.439453125

After this patch:
  # ls /sys/bus/iio/devices/iio:device0/in_voltage*_raw | wc -l
  2
  # cat /sys/bus/iio/devices/iio:device0/in_voltage_scale
  1.757812500

Link: https://lore.kernel.org/all/20260714131631.v2.1.0b846080833e4b836793c43fc26d1c6d817cf9b4@changeid/
Signed-off-by: Vladislav Leonov <vlad at zlab.su>
---
 drivers/iio/adc/rockchip_saradc.c | 16 ++++++++++++++++
 1 file changed, 16 insertions(+)

diff --git a/drivers/iio/adc/rockchip_saradc.c b/drivers/iio/adc/rockchip_saradc.c
index 0f0bf2906af0..5c45fae11890 100644
--- a/drivers/iio/adc/rockchip_saradc.c
+++ b/drivers/iio/adc/rockchip_saradc.c
@@ -348,6 +348,19 @@ static const struct rockchip_saradc_data rk3588_saradc_data = {
 	.read = rockchip_saradc_read_v2,
 };
 
+static const struct iio_chan_spec rockchip_rv1106_saradc_iio_channels[] = {
+	SARADC_CHANNEL(0, "adc0", 10),
+	SARADC_CHANNEL(1, "adc1", 10),
+};
+
+static const struct rockchip_saradc_data rv1106_saradc_data = {
+	.channels = rockchip_rv1106_saradc_iio_channels,
+	.num_channels = ARRAY_SIZE(rockchip_rv1106_saradc_iio_channels),
+	.clk_rate = 1000000,
+	.start = rockchip_saradc_start_v2,
+	.read = rockchip_saradc_read_v2,
+};
+
 static const struct of_device_id rockchip_saradc_match[] = {
 	{
 		.compatible = "rockchip,saradc",
@@ -370,6 +383,9 @@ static const struct of_device_id rockchip_saradc_match[] = {
 	}, {
 		.compatible = "rockchip,rk3588-saradc",
 		.data = &rk3588_saradc_data,
+	}, {
+		.compatible = "rockchip,rv1106-saradc",
+		.data = &rv1106_saradc_data,
 	},
 	{ }
 };
-- 
2.47.3