linux-kernel - Re: [PATCH v4 01/13] iio: dac: ds4424: reject -128 RAW value

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Message-ID: <aYHN3YfKCgEnAfD5@pengutronix.de>
Date: Tue, 3 Feb 2026 11:28:45 +0100
From: Oleksij Rempel <o.rempel@...gutronix.de>
To: Andy Shevchenko <andriy.shevchenko@...el.com>
Cc: Andy Shevchenko <andy@...nel.org>, Rob Herring <robh@...nel.org>,
	Conor Dooley <conor+dt@...nel.org>, devicetree@...r.kernel.org,
	linux-iio@...r.kernel.org, linux-kernel@...r.kernel.org,
	stable@...r.kernel.org, Nuno Sá <nuno.sa@...log.com>,
	kernel@...gutronix.de, David Jander <david@...tonic.nl>,
	Krzysztof Kozlowski <krzk+dt@...nel.org>,
	David Lechner <dlechner@...libre.com>,
	Jonathan Cameron <jic23@...nel.org>
Subject: Re: [PATCH v4 01/13] iio: dac: ds4424: reject -128 RAW value

On Tue, Feb 03, 2026 at 11:54:35AM +0200, Andy Shevchenko wrote:
> On Tue, Feb 03, 2026 at 10:34:21AM +0100, Oleksij Rempel wrote:
> > The DS442x DAC uses sign-magnitude encoding, so -128 cannot be represented
> > in hardware (7-bit magnitude).
> > 
> > Previously, passing -128 resulted in a truncated value that programmed
> > 0mA (magnitude 0) instead of the expected maximum negative current,
> > effectively failing silently.
> > 
> > Reject -128 to avoid producing the wrong current.
> 
> ...
> 
> >  	case IIO_CHAN_INFO_RAW:
> > -		if (val < S8_MIN || val > S8_MAX)
> > +		if (val <= S8_MIN || val > S8_MAX)
> >  			return -EINVAL;
> 
> I still consider using -127, 127 is better than type _MIN/_MAX.
> This is all due to '='.

The use of S8_MIN here is intentional to satisfy the requirement for a minimal
stable backport, as requested by Jonathan:
https://lore.kernel.org/all/20260201144226.218a43cb@jic23-huawei/

This patch: Strict "Fix only" for stable. Uses minimal logic changes (<=
S8_MIN) to avoid introducing new bugs during backporting.

N++ patch: Full refactoring.

Can we accept this temporary state to facilitate the stable process?

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