linux-kernel - Re: [PATCH v4 2/2] iio: adc: Add ti-ads1018 driver

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Message-ID: <aS_7xrMwW42qolG4@smile.fi.intel.com>
Date: Wed, 3 Dec 2025 10:58:46 +0200
From: Andy Shevchenko <andriy.shevchenko@...el.com>
To: Kurt Borja <kuurtb@...il.com>
Cc: Jonathan Cameron <jic23@...nel.org>, Rob Herring <robh@...nel.org>,
	Krzysztof Kozlowski <krzk+dt@...nel.org>,
	Conor Dooley <conor+dt@...nel.org>,
	Tobias Sperling <tobias.sperling@...ting.com>,
	David Lechner <dlechner@...libre.com>,
	Nuno Sá <nuno.sa@...log.com>,
	Andy Shevchenko <andy@...nel.org>, linux-iio@...r.kernel.org,
	devicetree@...r.kernel.org, linux-kernel@...r.kernel.org,
	Jonathan Cameron <Jonathan.Cameron@...wei.com>
Subject: Re: [PATCH v4 2/2] iio: adc: Add ti-ads1018 driver

On Tue, Dec 02, 2025 at 11:56:19PM -0500, Kurt Borja wrote:
> Add ti-ads1018 driver for Texas Instruments ADS1018 and ADS1118 SPI
> analog-to-digital converters.
> 
> These chips' MOSI pin is shared with a data-ready interrupt. Defining
> this interrupt in devicetree is optional, therefore we only create an
> IIO trigger if one is found.
> 
> Handling this interrupt requires some considerations. When enabling the
> trigger the CS line is tied low (active), thus we need to hold
> spi_bus_lock() too, to avoid state corruption. This is done inside the
> set_trigger_state() callback, to let users use other triggers without
> wasting a bus lock.

...

> +/**
> + * ADS1018_FSR_TO_SCALE - Converts FSR into scale
> + * @_fsr: Full-scale range in millivolts
> + * @_res: ADC resolution
> + *
> + * The macro is crafted to avoid potential overflows on 32-bit machines. This
> + * imposes restrictions on the possible values for @_fsr (less than 274878),

> + * and @_res (greater than or equal to 6 bits).

This is actually incorrect. See below.

> + * Return: Scale in IIO_VAL_INT_PLUS_NANO format
> + */
> +#define ADS1018_FSR_TO_SCALE(_fsr, _res) \
> +	{ 0, ((_fsr) * (MICRO >> 6)) / (BIT((_res) - 1) >> 6) }

This is different from what I suggested. But I think I was mistaken with
the parentheses and thought that you are dividing on the mask-like value.

If the current version correct by the result, first of all, the limitation for
@_res is 7 and not 6. And second, it can be rewritten in a simpler form.

	{ 0, ((_fsr) * (MICRO >> 6)) >> ((_res) - 6 - 1) }

Please, check it again.

-- 
With Best Regards,
Andy Shevchenko