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[2600:3c18:e002:2e11::c424]) by smtp.gmail.com with ESMTPSA id ffacd0b85a97d-4887a30bcc4sm1691360f8f.1.2026.09.24.13.53.33 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Thu, 24 Sep 2026 13:53:37 -0700 (PDT) From: Ridham Khurana To: Guenter Roeck Cc: linux-hwmon@vger.kernel.org, linux-kernel@vger.kernel.org, Christian Lamparter , Alexander Sverdlin , Nikita Shubin , Shuah Khan , Jori Koolstra , Brigham Campbell , linux-kernel-mentees@lists.linux.dev, Ridham Khurana Subject: [PATCH] hwmon: (lm70) Fix rounding of negative temperatures Date: Thu, 24 Sep 2026 20:53:23 +0000 Message-ID: <20260924205326.1739229-1-khurana.ridham222@gmail.com> X-Mailer: git-send-email 2.47.3 Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Transfer-Encoding: 8bit temp1_input_show() drops the low bits of the temperature register by dividing the raw value (raw / 32 on the LM70). These bits are not part of the temperature: the LM70, LM71, LM74 and TMP122/TMP124 always return some of them as 1, and the TMP125 fills them with copies of the temperature LSB. Division rounds toward zero, so a negative temperature with any of these bits set is reported one LSB too high. For example, the TMP122 returns 0xffff for -0.0625 degrees C, which the driver reports as 0. The LM70 returns 0xf39f for -25 degrees C, which the driver reports as -24750. Use an arithmetic right shift instead, which drops the low bits and rounds down. tmp421 had a similar problem with negative values, fixed by commit 724e8af85854 ("hwmon: (tmp421) fix rounding for negative values"). Fixes: e1a8e913f97e ("[PATCH] lm70: New hardware monitoring driver") Fixes: a86e94dc946d ("hwmon: (lm70) Add support for LM71 and LM74") Fixes: cd929672a9ef ("hwmon: (lm70) Add ti,tmp125 support") Signed-off-by: Ridham Khurana --- Build-tested on arm64 and arm (ep93xx_defconfig) with CONFIG_SENSORS_LM70=m. Tested in QEMU (arm64 and arm) with a stub SPI controller returning the datasheet register values; not tested on hardware. drivers/hwmon/lm70.c | 8 ++++---- 1 file changed, 4 insertions(+), 4 deletions(-) diff --git a/drivers/hwmon/lm70.c b/drivers/hwmon/lm70.c index 8b525725fef4..b29bac7a4cc1 100644 --- a/drivers/hwmon/lm70.c +++ b/drivers/hwmon/lm70.c @@ -96,21 +96,21 @@ static ssize_t temp1_input_show(struct device *dev, */ switch (p_lm70->chip) { case LM70_CHIP_LM70: - val = ((int)raw / 32) * 250; + val = ((int)raw >> 5) * 250; break; case LM70_CHIP_TMP121: case LM70_CHIP_TMP122: case LM70_CHIP_LM74: - val = ((int)raw / 8) * 625 / 10; + val = ((int)raw >> 3) * 625 / 10; break; case LM70_CHIP_LM71: - val = ((int)raw / 4) * 3125 / 100; + val = ((int)raw >> 2) * 3125 / 100; break; case LM70_CHIP_TMP125: - val = (sign_extend32(raw, 14) / 32) * 250; + val = (sign_extend32(raw, 14) >> 5) * 250; break; } -- 2.47.3