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([116.72.73.183]) by smtp.gmail.com with ESMTPSA id d2e1a72fcca58-835158a8432sm1014523b3a.20.2026.04.30.18.30.52 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Thu, 30 Apr 2026 18:30:55 -0700 (PDT) From: Tabrez Ahmed To: Guenter Roeck Cc: linux-hwmon@vger.kernel.org, linux-kernel@vger.kernel.org, shuah@kernel.org, me@brighamcampbell.com, Tabrez Ahmed , Sashiko Subject: [PATCH v4 1/3] hwmon: (ads7871) Fix endianness bug in 16-bit register reads Date: Fri, 1 May 2026 07:00:41 +0530 Message-ID: <20260501013044.22756-2-tabreztalks@gmail.com> X-Mailer: git-send-email 2.43.0 In-Reply-To: <20260501013044.22756-1-tabreztalks@gmail.com> References: <20260501013044.22756-1-tabreztalks@gmail.com> Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Transfer-Encoding: 8bit The ads7871_read_reg16() function relies on spi_w8r16() to read the 16-bit sensor output. The ADS7871 device transmits the Least Significant Byte (LSB) first. On Little-Endian architectures, spi_w8r16() correctly reconstructs the 16-bit value. However, on Big-Endian architectures, the byte swapping causes the first received byte (LSB) to be placed in the most significant byte of the u16, resulting in corrupted voltage readings. Replace spi_w8r16() with a manual spi_write_then_read() into a byte array, and safely reconstruct the integer using get_unaligned_le16() to ensure correct behavior across all architectures. Additionally, use a u8 variable for the command byte to ensure the correct instruction is transmitted on Big-Endian systems. Reported-by: Sashiko Closes: https://sashiko.dev/#/patchset/20260418034601.90226-1-tabreztalks@gmail.com Signed-off-by: Tabrez Ahmed --- drivers/hwmon/ads7871.c | 13 +++++++++++-- 1 file changed, 11 insertions(+), 2 deletions(-) diff --git a/drivers/hwmon/ads7871.c b/drivers/hwmon/ads7871.c index 9bfdf9e6bcd77..15104d9b2b733 100644 --- a/drivers/hwmon/ads7871.c +++ b/drivers/hwmon/ads7871.c @@ -59,6 +59,7 @@ #include #include #include +#include #define DEVICE_NAME "ads7871" @@ -77,9 +78,17 @@ static int ads7871_read_reg8(struct spi_device *spi, int reg) static int ads7871_read_reg16(struct spi_device *spi, int reg) { int ret; + u8 tx_cmd; + u8 rx_buf[2]; + reg = reg | INST_READ_BM | INST_16BIT_BM; - ret = spi_w8r16(spi, reg); - return ret; + tx_cmd = reg; + + ret = spi_write_then_read(spi, &tx_cmd, 1, rx_buf, 2); + if (ret < 0) + return ret; + + return get_unaligned_le16(rx_buf); } static int ads7871_write_reg8(struct spi_device *spi, int reg, u8 val) -- 2.43.0