linux-kernel - Re: [PATCH v2 6/8] iio: dac: ds4424: fix -128 rejection and refactor raw access

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Message-ID: <aXiWkF04r7FkLPRx@smile.fi.intel.com>
Date: Tue, 27 Jan 2026 12:42:24 +0200
From: Andy Shevchenko <andriy.shevchenko@...el.com>
To: Oleksij Rempel <o.rempel@...gutronix.de>
Cc: Jonathan Cameron <jic23@...nel.org>, Rob Herring <robh@...nel.org>,
	Krzysztof Kozlowski <krzk+dt@...nel.org>,
	Conor Dooley <conor+dt@...nel.org>, stable@...r.kernel.org,
	kernel@...gutronix.de, linux-kernel@...r.kernel.org,
	linux-iio@...r.kernel.org, devicetree@...r.kernel.org,
	Andy Shevchenko <andy@...nel.org>,
	David Lechner <dlechner@...libre.com>,
	Nuno Sá <nuno.sa@...log.com>,
	David Jander <david@...tonic.nl>
Subject: Re: [PATCH v2 6/8] iio: dac: ds4424: fix -128 rejection and refactor
 raw access

On Tue, Jan 27, 2026 at 07:09:37AM +0100, Oleksij Rempel wrote:
> The DS442x DAC uses sign-magnitude encoding, so -128 cannot be represented.
> Previously, passing -128 resulted in a truncated value that programmed 0mA.
> 
> Fix this by validating the input against the 7-bit magnitude limit.
> Additionally, refactor the raw access logic to use symmetrical bitwise
> operations, replacing the union structure.

> Fixes: d632a2bd8ffc ("iio: dac: ds4422/ds4424 dac driver")

Usually fixes go first in the series...

...

> +#define DS4424_DAC_MASK			GENMASK(6, 0)
> +#define DS4424_DAC_SOURCE		BIT(7)

+ bits.h ?

...

>  	case IIO_CHAN_INFO_RAW:
> -		if (val < S8_MIN || val > S8_MAX)
> +		abs_val = abs(val);

> +

Redundant blank line.

> +		if (abs_val > DS4424_DAC_MASK)
>  			return -EINVAL;

...

> +		/*
> +		 * Currents exiting the IC (Source) are positive.
> +		 * Canonicalize 0 to sink; datasheet treats sign as don't-care.
> +		 */
> +		if (val > 0)
> +			abs_val |= DS4424_DAC_SOURCE;

Hmm... Maybe 0 should be excluded as invalid?

-- 
With Best Regards,
Andy Shevchenko