Re: [PATCH v4 01/13] iio: dac: ds4424: reject -128 RAW value
From: Oleksij Rempel <o.rempel@pengutronix.de>
Date: 2026-02-03 10:28:51
Also in:
linux-iio, lkml, stable
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:quoted
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....quoted
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/ (local) 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? -- Pengutronix e.K. | | Steuerwalder Str. 21 | http://www.pengutronix.de/ | 31137 Hildesheim, Germany | Phone: +49-5121-206917-0 | Amtsgericht Hildesheim, HRA 2686 | Fax: +49-5121-206917-5555 |