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

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Message-ID: <aXiYIYd08vFfLoIQ@pengutronix.de>
Date: Tue, 27 Jan 2026 11:49:05 +0100
From: Oleksij Rempel <o.rempel@...gutronix.de>
To: Andy Shevchenko <andriy.shevchenko@...el.com>
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 12:42:24PM +0200, Andy Shevchenko wrote:
> 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")
> > +		/*
> > +		 * 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?

0 is valid value for no current flow (power off). The direction bit
DS4424_DAC_SOURCE  will just make no difference if value is 0.

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