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

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Message-ID: <b4a86788-fe0e-483c-93ff-fe993edb3181@oss.qualcomm.com>
Date: Fri, 31 Oct 2025 10:00:25 +0100
From: Konrad Dybcio <konrad.dybcio@....qualcomm.com>
To: Antony Kurniawan Soemardi <linux@...nkusors.com>,
        Jonathan Cameron <jic23@...nel.org>,
        David Lechner <dlechner@...libre.com>,
        Nuno Sá <nuno.sa@...log.com>,
        Andy Shevchenko <andy@...nel.org>,
        Dmitry Baryshkov <dmitry.baryshkov@....qualcomm.com>
Cc: 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 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?

Konrad