linux-kernel - [PATCH 2/2] iio: adc: qcom-pm8xxx-xoadc: fix incorrect calibration values

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Message-Id: <20251028-pm8xxx-xoadc-fix-v1-2-b000e1036e41@smankusors.com>
Date: Mon, 27 Oct 2025 17:29:18 +0000 (UTC)
From: Antony Kurniawan Soemardi <linux@...nkusors.com>
To: Jonathan Cameron <jic23@...nel.org>, 
 David Lechner <dlechner@...libre.com>, 
 Nuno Sá <nuno.sa@...log.com>, 
 Andy Shevchenko <andy@...nel.org>
Cc: linux-arm-msm@...r.kernel.org, linux-iio@...r.kernel.org, 
 linux-kernel@...r.kernel.org, 
 Antony Kurniawan Soemardi <linux@...nkusors.com>
Subject: [PATCH 2/2] iio: adc: qcom-pm8xxx-xoadc: fix incorrect calibration
 values

On msm8960 phones, the XOADC driver was using incorrect calibration
values:
absolute calibration dx = 625000 uV, dy = 4 units
ratiometric calibration dx = 1800, dy = -29041 units

As a result, reading from the IIO bus returned unexpected results:
in_voltage_7 (USB_VBUS): 0
in_voltage_10 (125V): 0

The issue was caused by not setting the ratiometric scale (amux_ip_rsv)
from the predefined channels. Additionally, the downstream code always
set the ADC_ARB_USRP_DIG_PARAM register to PM8XXX_ADC_ARB_ANA_DIG [1].
That value does not include the SEL_SHIFT0 and SEL_SHIFT1 bits. Enabling
those bits caused calibration errors too, so they were removed.

With these fixes, calibration now uses the correct values:
absolute calibration dx = 625000 uV, dy = 6307 units
ratiometric calibration dx = 1800, dy = 18249 units

Reading from the IIO bus now returns expected results:
in_voltage_7 (USB_VBUS): 4973836
in_voltage_10 (125V): 1249405

[1] https://github.com/LineageOS/android_kernel_sony_msm8960t/blob/93319b1e5aa343ec1c1aabcb028c5e88c7df7c01/drivers/hwmon/pm8xxx-adc.c#L407-L408

Signed-off-by: Antony Kurniawan Soemardi <linux@...nkusors.com>
---
 drivers/iio/adc/qcom-pm8xxx-xoadc.c | 10 ++++++----
 1 file changed, 6 insertions(+), 4 deletions(-)

diff --git a/drivers/iio/adc/qcom-pm8xxx-xoadc.c b/drivers/iio/adc/qcom-pm8xxx-xoadc.c
index 8555f34036fb13c41ac720dc02c1dc39876e9198..a53d361456ec36b66d258041877bd96ab37838c4 100644
--- a/drivers/iio/adc/qcom-pm8xxx-xoadc.c
+++ b/drivers/iio/adc/qcom-pm8xxx-xoadc.c
@@ -503,10 +503,11 @@ static int pm8xxx_read_channel_rsv(struct pm8xxx_xoadc *adc,
 		goto unlock;
 
 	/* Decimation factor */
-	ret = regmap_write(adc->map, ADC_ARB_USRP_DIG_PARAM,
-			   ADC_ARB_USRP_DIG_PARAM_SEL_SHIFT0 |
-			   ADC_ARB_USRP_DIG_PARAM_SEL_SHIFT1 |
-			   ch->decimation << ADC_DIG_PARAM_DEC_SHIFT);
+	ret = regmap_update_bits(adc->map,
+				 ADC_ARB_USRP_DIG_PARAM,
+				 ADC_ARB_USRP_DIG_PARAM_DEC_RATE0 |
+				 ADC_ARB_USRP_DIG_PARAM_DEC_RATE1,
+				 ch->decimation << ADC_DIG_PARAM_DEC_SHIFT);
 	if (ret)
 		goto unlock;
 
@@ -783,6 +784,7 @@ static int pm8xxx_xoadc_parse_channel(struct device *dev,
 	ch->calibration = VADC_CALIB_ABSOLUTE;
 	/* Everyone seems to use default ("type 2") decimation */
 	ch->decimation = VADC_DEF_DECIMATION;
+	ch->amux_ip_rsv = hwchan->amux_ip_rsv;
 
 	if (!fwnode_property_read_u32(fwnode, "qcom,ratiometric", &rsv)) {
 		ch->calibration = VADC_CALIB_RATIOMETRIC;

-- 
2.34.1