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

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Message-ID: <003c5cf7-2498-4ff3-a8b4-2911941b1464@smankusors.com>
Date: Mon, 27 Oct 2025 19:53:37 +0000 (UTC)
From: Antony Kurniawan Soemardi <linux@...nkusors.com>
To: David Lechner <dlechner@...libre.com>, Jonathan Cameron
 <jic23@...nel.org>, 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, linux@...nkusors.com
Subject: Re: [PATCH 2/2] iio: adc: qcom-pm8xxx-xoadc: fix incorrect
 calibration values

On 10/28/2025 1:35 AM, David Lechner wrote:
> On 10/27/25 12:29 PM, Antony Kurniawan Soemardi wrote:
>> 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
> Mentioning downstream kernels is usually a red flag. :-)
>
> We can justify it here though by saying that there is no documentation
> available other than downstream source code, so we are just using it
> as a reference.
ah ok, rewording needed then
>> 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
> Would be useful to mention which hardware you tested with in case
> it turns out that there is some other hardware that does require the
> SHIFT0/1 bits to be set.
I did mention Sony Xperia SP from cover letter, but I haven't
referenced it in this commit yet. Also I tried to search on Github for
SHIFT0/1 bits, but couldn't find any usage of them...
>> [1] https://github.com/LineageOS/android_kernel_sony_msm8960t/blob/93319b1e5aa343ec1c1aabcb028c5e88c7df7c01/drivers/hwmon/pm8xxx-adc.c#L407-L408
>>
> Since this is a fix, it should have a Fixes: tag. And it sounds like
> possibly two separate fixes. In that case, it should be two separate
> patches.
Fixes into 63c3ecd946d4ae2879ec0d8c6dcb90132a74d831?
>> 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);
> As a follow-up patch, it would be nice to update the driver to use FIELD_PREP().
>
> I.e. remove ADC_ARB_USRP_DIG_PARAM_DEC_RATE0, ADC_ARB_USRP_DIG_PARAM_DEC_RATE1
> and ADC_DIG_PARAM_DEC_SHIFT macros and replace them with one macro:
>
> #define ADC_ARB_USRP_DIG_PARAM_DEC_RATE		GENMASK(6, 5)
>
> Then use it like:
>
> 	ret = regmap_update_bits(adc->map,
> 				 ADC_ARB_USRP_DIG_PARAM,
> 				 ADC_ARB_USRP_DIG_PARAM_DEC_RATE,
> 				 FIELD_PREP(ADC_ARB_USRP_DIG_PARAM_DEC_RATE,
> 					    ch->decimation));
>
> This should be done for all of the similar multi-bit fields.
as a follow up patch, you mean next version of this patch series, or
separate patch series?
>>   	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;
>>