linux-kernel - Re: [PATCH 2/4] iio: adc: ad4695: implement calibration support

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Message-ID: <20240821141615.00006ebe@Huawei.com>
Date: Wed, 21 Aug 2024 14:16:15 +0100
From: Jonathan Cameron <Jonathan.Cameron@...wei.com>
To: David Lechner <dlechner@...libre.com>
CC: Jonathan Cameron <jic23@...nel.org>, Michael Hennerich
	<Michael.Hennerich@...log.com>, Nuno Sá
	<nuno.sa@...log.com>, Jonathan Corbet <corbet@....net>,
	<linux-iio@...r.kernel.org>, <linux-kernel@...r.kernel.org>,
	<linux-doc@...r.kernel.org>
Subject: Re: [PATCH 2/4] iio: adc: ad4695: implement calibration support

On Tue, 20 Aug 2024 10:58:36 -0500
David Lechner <dlechner@...libre.com> wrote:

> The AD4695 has a calibration feature that allows the user to compensate
> for variations in the analog front end. This implements this feature in
> the driver using the standard `calibgain` and `calibbias` attributes.
> 
> Signed-off-by: David Lechner <dlechner@...libre.com>
Hi David,

Whilst some of the messy value manipulation is unavoidable
(oh for signed integer zero!), I wonder if we can at least
move one case into the core.

See below.

> +
> +static int ad4695_write_raw(struct iio_dev *indio_dev,
> +			    struct iio_chan_spec const *chan,
> +			    int val, int val2, long mask)
> +{
> +	struct ad4695_state *st = iio_priv(indio_dev);
> +	unsigned int reg_val;
> +	int ret;
> +
> +	iio_device_claim_direct_scoped(return -EBUSY, indio_dev) {
> +		switch (mask) {
> +		case IIO_CHAN_INFO_CALIBSCALE:
> +			switch (chan->type) {
> +			case IIO_VOLTAGE:
> +				if (val < 0 || val2 < 0)
> +					reg_val = 0;
> +				else if (val > 1)
> +					reg_val = U16_MAX;
> +				else
> +					reg_val = (val * (1 << 16) +
> +						   mul_u64_u32_div(val2, 1 << 16,
> +								   MICRO)) / 2;
Maybe worth extending iio_write_channel_info() to handle
IIO_VAL_FRACTIONAL_LOG2()?
It'll look much like this and you'll need to provide write_raw_get_fmt()
so the core know what to do with the value formatting.

I don't really like the mixture here between the read path being able
to rely on the core code to deal with the /2^X and the write path not.
> +
> +				return regmap_write(st->regmap16,
> +					AD4695_REG_GAIN_IN(chan->scan_index),
> +					reg_val);
> +			default:
> +				return -EINVAL;