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Sat, 08 Aug 2026 01:37:24 -0700 (PDT) Received: from SGN-LDSENG.tasernet.com ([2405:4800:5cc3:11a:1ac0:4dff:fe8b:4a69]) by smtp.gmail.com with ESMTPSA id 5a478bee46e88-315be86d3fcsm16736028eec.4.2026.08.08.01.37.22 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Sat, 08 Aug 2026 01:37:23 -0700 (PDT) From: Cong Nguyen To: Guenter Roeck , Vadim Pasternak Cc: linux-hwmon@vger.kernel.org, linux-kernel@vger.kernel.org Subject: [PATCH] hwmon: (max6621) fix negative temperature offset and crit readings Date: Sat, 8 Aug 2026 15:37:18 +0700 Message-Id: <20260808083718.2612205-1-congnt264@gmail.com> X-Mailer: git-send-email 2.25.1 Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Transfer-Encoding: 8bit max6621_read() reads the temperature input, offset and critical alert registers into a u32 and assigns them to the output without sign extension. The device reports these values in two's complement (the driver comment and the write path, which clamps to MAX6621_TEMP_INPUT_MIN == -127000 and encodes negatives, both rely on this), so negative values are misreported as large positive numbers: - temp_offset: *val = (regval >> MAX6621_REG_TEMP_SHIFT) * 1000, an unsigned shift, so e.g. a -10 degrees C offset (register 0xfd80) reads back as ~+1014000 millidegrees. - temp_crit: *val = regval * 1000, so a negative critical threshold reads back as a large positive value. - temp_input used an s8 intermediate, which is correct for the -127..127 range but reports the documented +128 degrees C maximum as -128 degrees C. The registers are 16-bit (the driver's own PECI error codes occupy 0x8000-0x80ff), so sign-extend from bit 15 before scaling. This fixes all three reads and drops the now-unused s8 intermediate. 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 --- drivers/hwmon/max6621.c | 11 +++++------ 1 file changed, 5 insertions(+), 6 deletions(-) diff --git a/drivers/hwmon/max6621.c b/drivers/hwmon/max6621.c index a7066f3a0bb4..03ac3eb5a594 100644 --- a/drivers/hwmon/max6621.c +++ b/drivers/hwmon/max6621.c @@ -204,7 +204,6 @@ max6621_read(struct device *dev, enum hwmon_sensor_types type, u32 attr, struct max6621_data *data = dev_get_drvdata(dev); u32 regval; int reg; - s8 temp; int ret; switch (type) { @@ -225,8 +224,8 @@ max6621_read(struct device *dev, enum hwmon_sensor_types type, u32 attr, * The temperature is given in two's complement and 8 * bits is used for the register conversion. */ - temp = (regval >> MAX6621_REG_TEMP_SHIFT); - *val = temp * 1000L; + *val = (sign_extend32(regval, 15) >> + MAX6621_REG_TEMP_SHIFT) * 1000L; break; case hwmon_temp_offset: @@ -239,8 +238,8 @@ max6621_read(struct device *dev, enum hwmon_sensor_types type, u32 attr, if (ret) return ret; - *val = (regval >> MAX6621_REG_TEMP_SHIFT) * - 1000L; + *val = (sign_extend32(regval, 15) >> + MAX6621_REG_TEMP_SHIFT) * 1000L; break; case hwmon_temp_crit: @@ -254,7 +253,7 @@ max6621_read(struct device *dev, enum hwmon_sensor_types type, u32 attr, if (ret) return ret; - *val = regval * 1000L; + *val = sign_extend32(regval, 15) * 1000L; break; case hwmon_temp_crit_alarm: -- 2.25.1