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Mon, 10 Aug 2026 09:26:13 -0700 (PDT) Sender: Guenter Roeck Date: Mon, 10 Aug 2026 09:26:12 -0700 From: Guenter Roeck To: Cong Nguyen Cc: Vadim Pasternak , linux-hwmon@vger.kernel.org, linux-kernel@vger.kernel.org, stable@vger.kernel.org Subject: Re: [PATCH v2 2/2] hwmon: (max6621) fix negative temperature offset and crit readings Message-ID: References: <9d3a4f1895a47794bb359a2a32fb1ccd6a15812c.1786334038.git.congnt264@gmail.com> Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: On Mon, Aug 10, 2026 at 11:28:39AM +0700, Cong Nguyen wrote: > max6621_read() reads the CONFIG2 offset and the critical alert threshold > registers into a u32 and scales them without sign extension: > > /* offset */ *val = (regval >> MAX6621_REG_TEMP_SHIFT) * 1000L; > /* crit */ *val = regval * 1000L; > > Both attributes are writable and their write paths clamp to a negative > minimum and encode negative values, so a value written as negative is read > back as a large positive number. For example, writing a -10 degrees C > offset stores max6621_temp_mc2reg(-10000) = (-10 << 6) = 0xfd80; the read > then computes 0xfd80 >> 6 = 1014 -> 1014000 instead of -10000. > > Cast the register value to s16 before scaling so the read preserves the > sign the write path encodes. The temperature input path already uses an s8 > intermediate and is left unchanged. > > Fixes: 92b64580f14b ("hwmon: (max6621) Add support for Maxim MAX6621 temperature sensor") > Cc: stable@vger.kernel.org > Assisted-by: Claude:claude-opus-4 > Signed-off-by: Cong Nguyen Applied. Thanks, Guenter