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

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Message-ID: <60245ae3-c489-4dea-9252-3a200fb6f6e0@smankusors.com>
Date: Sun, 11 Jan 2026 17:31:45 +0000 (UTC)
From: Antony Kurniawan Soemardi <linux@...nkusors.com>
To: Dmitry Baryshkov <dmitry.baryshkov@....qualcomm.com>,
 Konrad Dybcio <konrad.dybcio@....qualcomm.com>
Cc: Jonathan Cameron <jic23@...nel.org>, David Lechner
 <dlechner@...libre.com>, Nuno Sá <nuno.sa@...log.com>,
 Andy Shevchenko <andy@...nel.org>, linux-arm-msm@...r.kernel.org,
 linux-iio@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH 2/2] iio: adc: qcom-pm8xxx-xoadc: fix incorrect
 calibration values

On 11/1/2025 4:25 PM, Dmitry Baryshkov wrote:
> On Fri, Oct 31, 2025 at 10:00:25AM +0100, Konrad Dybcio wrote:
>> On 10/30/25 5:57 PM, Antony Kurniawan Soemardi wrote:
>>> On 10/28/2025 4:44 PM, Konrad Dybcio wrote:
>>>> On 10/27/25 6:29 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
>>>>> 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,
>>>> The PM8921 datasheet suggests a single valid value of BIT(5)=1, BIT(6)=0
>>>> for a "1K" (1/1024?) ratio, although a comment in this file suggests
>>>> BIT(5)|BIT(6) is also valid and corresponds to 1/4096.. I wouldn't be
>>>> surprised if that is the case
>>>>
>>>> The previously set bits are a field called DECI_SEL but are otherwise left
>>>> undescribed
>>> So, do you think we can leave the BIT(0) and BIT(1) as is? I have a feeling
>>> that if they aren't set, these changes might prevent the APQ8060 Dragonboard
>>> from reading the cm3605 sensor? or maybe not?
>>>
>>> I mean this one, since the driver was originally tested on that board
>>> https://github.com/torvalds/linux/blob/e53642b87a4f4b03a8d7e5f8507fc3cd0c595ea6/arch/arm/boot/dts/qcom/qcom-apq8060-dragonboard.dts#L67-L79
>> +Dmitry would you have that (or similar) board in your museum?
> I do, but I sadly I didn't test it lately (nor do I remember if I have
> sensors board or not). I can try testing it next week, if I have time.
>
Hi Dmitry, I wanted to follow up and ask whether you’ve had a chance to 
test the APQ8060 DragonBoard though?

(Also happy new year! Eh, it's 12 days late...)

Thanks,