Re: [PATCH 3/5] iio: adc: qcom-spmi-adc5: Add ADC5_BAT_THERM_100K_PU

["Luca Weiss" <luca.weiss@fairphone.com>]

Hi Val,

On Thu Nov 12, 2026 at 6:07 PM CET, Val Packett wrote:
> Even though it existed in bindings for the longest time,
> ADC5_BAT_THERM_100K_PU was never assigned in the driver. Do so.
>
> Signed-off-by: Val Packett <val@packett.cool>
> ---
>  drivers/iio/adc/qcom-spmi-adc5.c | 2 ++
>  1 file changed, 2 insertions(+)
>
> diff --git a/drivers/iio/adc/qcom-spmi-adc5.c b/drivers/iio/adc/qcom-spmi-adc5.c
> index d57ba8526e0c..c27ff89429f5 100644
> --- a/drivers/iio/adc/qcom-spmi-adc5.c
> +++ b/drivers/iio/adc/qcom-spmi-adc5.c
> @@ -542,6 +542,8 @@ static const struct adc5_channels adc5_chans_pmic[ADC5_MAX_CHANNEL] = {
>  					SCALE_HW_CALIB_DEFAULT)
>  	[ADC5_XO_THERM_100K_PU]	= ADC5_CHAN_TEMP("xo_therm", 0,
>  					SCALE_HW_CALIB_XOTHERM)
> +	[ADC5_BAT_THERM_100K_PU]	= ADC5_CHAN_TEMP("bat_therm", 0,
> +					SCALE_HW_CALIB_THERM_100K_PULLUP)

While this will work fine for some devices, unfortunately this won't
work for quite some other devices that don't use a 30K, 100K or 400K
NTC in the battery - or when the NTC beta (B) is differing to the
hardcoded lookup table.

For example on Fairphone 4 (pm7250b fwiw), the battery has a 10kΩ NTC,
so using the ADC5_BAT_THERM_30K_PU with the hard-coded lookup tables
would result in very wrong temperature values. Even ignoring the whole
NTC beta topic.

You can see my proposed patch series at
https://lore.kernel.org/linux-arm-msm/20260220-bat-temp-adc-v2-0-fe34ed4ea851@fairphone.com/

Unfortunately it's from February and I haven't spent more time on this
topic since then, mostly because fuel gauge anyways was downstream, so
pushing just this upstream wouldn't make much difference.

Now it does, so I should get back to it... Let me know your thoughts!

(Fairphone 3 with SDM632/PMI632 would actually be fine-ish as-is because
the battery has a 100kΩ NTC and the beta probably is close enough to
what's in adcmap_100k_104ef_104fb_1875_vref)

Regards
Luca

>  	[ADC5_BAT_ID_100K_PU]	= ADC5_CHAN_TEMP("bat_id", 0,
>  					SCALE_HW_CALIB_DEFAULT)
>  	[ADC5_AMUX_THM1_100K_PU] = ADC5_CHAN_TEMP("amux_thm1_100k_pu", 0,