linux-kernel - Re: [PATCH 1/2] iio: adc: Add driver for Marvell 88PM886 PMIC ADC

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Message-ID: <960b23ff-827f-4ac6-a951-c61a0fec0c11@baylibre.com>
Date: Fri, 29 Aug 2025 10:52:32 -0500
From: David Lechner <dlechner@...libre.com>
To: Duje Mihanović <duje@...emihanovic.xyz>
Cc: Jonathan Cameron <jic23@...nel.org>, Nuno Sá
 <nuno.sa@...log.com>, Andy Shevchenko <andy@...nel.org>,
 Karel Balej <balejk@...fyz.cz>, Lee Jones <lee@...nel.org>,
 David Wronek <david@...nlining.org>, phone-devel@...r.kernel.org,
 ~postmarketos/upstreaming@...ts.sr.ht, linux-kernel@...r.kernel.org,
 linux-iio@...r.kernel.org
Subject: Re: [PATCH 1/2] iio: adc: Add driver for Marvell 88PM886 PMIC ADC

On 8/29/25 10:20 AM, Duje Mihanović wrote:
> On Friday, 29 August 2025 01:40:56 Central European Summer Time David Lechner wrote:

...

>>> +		*val = raw;
>>> +		dev_dbg(&iio->dev, "chan: %d, raw: %d\n", chan->channel, *val);
>>> +		ret = IIO_VAL_INT;
>>> +		break;
>>> +	case IIO_CHAN_INFO_PROCESSED: {
>>
>> Unusual to have both raw and processed. What is the motivation?
> 
> I was following what ab8500-gpadc does, no particular motivation.
> Considering the above, to me it makes the most sense to limit it to
> processed.
> 

In IIO, we generally prefer do the least amount of processing on
the value from the hardware, so IIO_CHAN_INFO_RAW is mostly used
and processed is only used in cases where there isn't linear scaling
or some other unusually thing going on.

So in this driver, processed probably makes sense for the resistance
channels since we have to do some calculation anyway, but for the
voltage channels, raw would be preferred.