linux-kernel - Re: [PATCH v4 2/2] iio: adc: Add TI ADS1100 and ADS1000

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Date:   Mon, 6 Mar 2023 15:29:37 +0200
From:   Andy Shevchenko <andriy.shevchenko@...ux.intel.com>
To:     Mike Looijmans <mike.looijmans@...ic.nl>
Cc:     devicetree@...r.kernel.org, linux-iio@...r.kernel.org,
        Caleb Connolly <caleb.connolly@...aro.org>,
        ChiYuan Huang <cy_huang@...htek.com>,
        ChiaEn Wu <chiaen_wu@...htek.com>,
        Cosmin Tanislav <demonsingur@...il.com>,
        Ibrahim Tilki <Ibrahim.Tilki@...log.com>,
        Jonathan Cameron <jic23@...nel.org>,
        Lars-Peter Clausen <lars@...afoo.de>,
        Marcus Folkesson <marcus.folkesson@...il.com>,
        Ramona Bolboaca <ramona.bolboaca@...log.com>,
        William Breathitt Gray <william.gray@...aro.org>,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH v4 2/2] iio: adc: Add TI ADS1100 and ADS1000

On Mon, Mar 06, 2023 at 02:13:12PM +0100, Mike Looijmans wrote:
> The ADS1100 is a 16-bit ADC (at 8 samples per second).
> The ADS1000 is similar, but has a fixed data rate.

...

> +	/* Value is always 16-bit 2's complement */
> +	value = be16_to_cpu(buffer);

+ Blank line?

> +	/* Shift result to compensate for bit resolution vs. sample rate */
> +	value <<= 16 - ads1100_data_bits(data);

+ Blank line?

> +	*val = sign_extend32(value, 15);

...

> +	microvolts = regulator_get_voltage(data->reg_vdd);
> +	/*
> +	 * val2 is in 'micro' units, n = val2 / 1000000
> +	 * result must be millivolts, d = microvolts / 1000
> +	 * the full-scale value is d/n, corresponds to 2^15,
> +	 * hence the gain = (d / n) >> 15, factoring out the 1000 and moving the
> +	 * bitshift so everything fits in 32-bits yields this formula.
> +	 */
> +	gain = ((microvolts + BIT(14)) >> 15) * 1000 / val2;

Perhaps adding MICROVOLT_PER_MILLIVOLT (to units.h) and use it here?

Besides that it's seems like

	microvolts = regulator_get_voltage(data->reg_vdd);
	gain = DIV_ROUNDUP_CLOSEST(microvolts, BIT(15)) *
	       MICROVOLT_PER_MILLIVOLT / val2;

> +	if (gain <= 0 || gain > 8)
> +		return -EINVAL;

As I commented out in the previous discussion (please, give a chance to the
reviewers to answer before issuing a new version of the series) this better
to be

	if (gain < BIT(0) || gain > BIT(3))

which will show the nature of power of two implicitly.

> +	regval = ffs(gain) - 1;
> +	ads1100_set_config_bits(data, ADS1100_PGA_MASK, regval);

Can be unified in one line.

> +	return 0;
> +}

...

> +			return ads1100_set_config_bits(
> +					data, ADS1100_DR_MASK,
> +					FIELD_PREP(ADS1100_DR_MASK, i));

Wrong indentation.
Please, check all your code for this kind of issues.

-- 
With Best Regards,
Andy Shevchenko