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[82.69.66.36]) by smtp.gmail.com with ESMTPSA id 5b1f17b1804b1-48a82301adesm114565645e9.10.2026.05.01.01.49.03 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Fri, 01 May 2026 01:49:03 -0700 (PDT) Date: Fri, 1 May 2026 09:49:02 +0100 From: David Laight To: Tabrez Ahmed Cc: Guenter Roeck , linux-hwmon@vger.kernel.org, linux-kernel@vger.kernel.org, shuah@kernel.org, me@brighamcampbell.com, Sashiko Subject: Re: [PATCH v5 1/3] hwmon: (ads7871) Fix endianness bug in 16-bit register reads Message-ID: <20260501094902.05ce6d37@pumpkin> In-Reply-To: <20260501023530.31160-2-tabreztalks@gmail.com> References: <20260501023530.31160-1-tabreztalks@gmail.com> <20260501023530.31160-2-tabreztalks@gmail.com> X-Mailer: Claws Mail 4.1.1 (GTK 3.24.38; arm-unknown-linux-gnueabihf) 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-Transfer-Encoding: 7bit On Fri, 1 May 2026 08:05:28 +0530 Tabrez Ahmed wrote: > 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 | 14 +++++++++++--- > 1 file changed, 11 insertions(+), 3 deletions(-) > > diff --git a/drivers/hwmon/ads7871.c b/drivers/hwmon/ads7871.c > index 9bfdf9e6bcd77..d77eff430935b 100644 > --- a/drivers/hwmon/ads7871.c > +++ b/drivers/hwmon/ads7871.c > @@ -59,9 +59,9 @@ > #include > #include > #include > +#include > > #define DEVICE_NAME "ads7871" > - > struct ads7871_data { > struct spi_device *spi; > }; > @@ -77,9 +77,17 @@ 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; Isn't it enough to just byteswap the result? so: return le16toh(ret); The whole thing can be: return le16toh(spi_w8r16(spi, reg | INST_READ_BM | INST_16BIT_BM)); (although I suspect sparse bleats and needs an annoying (__force __le16) cast) -- David > + 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)