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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: quoted-printable Content-Type: text/plain; charset="utf-8" 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@g= mail.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 =20 #define DEVICE_NAME "ads7871" =20 @@ -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 =3D reg | INST_READ_BM | INST_16BIT_BM; - ret =3D spi_w8r16(spi, reg); - return ret; + tx_cmd =3D reg; + + ret =3D spi_write_then_read(spi, &tx_cmd, 1, rx_buf, 2); + if (ret < 0) + return ret; + + return get_unaligned_le16(rx_buf); } =20 static int ads7871_write_reg8(struct spi_device *spi, int reg, u8 val) --=20 2.43.0 From nobody Tue Jun 16 14:50:18 2026 Received: from mail-pf1-f181.google.com (mail-pf1-f181.google.com [209.85.210.181]) (using TLSv1.2 with cipher ECDHE-RSA-AES128-GCM-SHA256 (128/128 bits)) (No client certificate requested) by smtp.subspace.kernel.org (Postfix) with ESMTPS id 7A0A42BE033 for ; 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([116.72.73.183]) by smtp.gmail.com with ESMTPSA id d2e1a72fcca58-835158a8432sm1014523b3a.20.2026.04.30.18.30.56 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Thu, 30 Apr 2026 18:30:58 -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 Subject: [PATCH v4 2/3] hwmon: (ads7871) Convert to hwmon_device_register_with_info Date: Fri, 1 May 2026 07:00:42 +0530 Message-ID: <20260501013044.22756-3-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: quoted-printable Content-Type: text/plain; charset="utf-8" Convert the ads7871 driver from the legacy hwmon_device_register() to the modern hwmon_device_register_with_info() API. This migration simplifies the driver by using the structured hwmon_channel_info approach and prepares the codebase for the transition to a shared DMA-safe buffer. While at it, fix checkpatch violations. Signed-off-by: Tabrez Ahmed --- drivers/hwmon/ads7871.c | 75 ++++++++++++++++++++++------------------- 1 file changed, 40 insertions(+), 35 deletions(-) diff --git a/drivers/hwmon/ads7871.c b/drivers/hwmon/ads7871.c index 15104d9b2b733..3ee04719eefd9 100644 --- a/drivers/hwmon/ads7871.c +++ b/drivers/hwmon/ads7871.c @@ -56,7 +56,6 @@ #include #include #include -#include #include #include #include @@ -67,6 +66,16 @@ struct ads7871_data { struct spi_device *spi; }; =20 +static umode_t ads7871_is_visible(const void *data, + enum hwmon_sensor_types type, + u32 attr, int channel) +{ + if (type =3D=3D hwmon_in && attr =3D=3D hwmon_in_input) + return 0444; + + return 0; +} + static int ads7871_read_reg8(struct spi_device *spi, int reg) { int ret; @@ -94,19 +103,20 @@ static int ads7871_read_reg16(struct spi_device *spi, = int reg) static int ads7871_write_reg8(struct spi_device *spi, int reg, u8 val) { u8 tmp[2] =3D {reg, val}; + return spi_write(spi, tmp, sizeof(tmp)); } =20 -static ssize_t voltage_show(struct device *dev, struct device_attribute *d= a, - char *buf) +static int ads7871_read(struct device *dev, enum hwmon_sensor_types type, + u32 attr, int channel, long *val) { struct ads7871_data *pdata =3D dev_get_drvdata(dev); struct spi_device *spi =3D pdata->spi; - struct sensor_device_attribute *attr =3D to_sensor_dev_attr(da); - int ret, val, i =3D 0; - uint8_t channel, mux_cnv; + int ret, raw_val, i =3D 0; + u8 mux_cnv; =20 - channel =3D attr->index; + if (type !=3D hwmon_in || attr !=3D hwmon_in_input) + return -EOPNOTSUPP; /* * TODO: add support for conversions * other than single ended with a gain of 1 @@ -136,39 +146,34 @@ static ssize_t voltage_show(struct device *dev, struc= t device_attribute *da, } =20 if (mux_cnv =3D=3D 0) { - val =3D ads7871_read_reg16(spi, REG_LS_BYTE); - if (val < 0) - return val; + raw_val =3D ads7871_read_reg16(spi, REG_LS_BYTE); + if (raw_val < 0) + return raw_val; + /*result in volts*10000 =3D (val/8192)*2.5*10000*/ - val =3D ((val >> 2) * 25000) / 8192; - return sysfs_emit(buf, "%d\n", val); + *val =3D ((raw_val >> 2) * 25000) / 8192; + return 0; } =20 return -ETIMEDOUT; } =20 -static SENSOR_DEVICE_ATTR_RO(in0_input, voltage, 0); -static SENSOR_DEVICE_ATTR_RO(in1_input, voltage, 1); -static SENSOR_DEVICE_ATTR_RO(in2_input, voltage, 2); -static SENSOR_DEVICE_ATTR_RO(in3_input, voltage, 3); -static SENSOR_DEVICE_ATTR_RO(in4_input, voltage, 4); -static SENSOR_DEVICE_ATTR_RO(in5_input, voltage, 5); -static SENSOR_DEVICE_ATTR_RO(in6_input, voltage, 6); -static SENSOR_DEVICE_ATTR_RO(in7_input, voltage, 7); - -static struct attribute *ads7871_attrs[] =3D { - &sensor_dev_attr_in0_input.dev_attr.attr, - &sensor_dev_attr_in1_input.dev_attr.attr, - &sensor_dev_attr_in2_input.dev_attr.attr, - &sensor_dev_attr_in3_input.dev_attr.attr, - &sensor_dev_attr_in4_input.dev_attr.attr, - &sensor_dev_attr_in5_input.dev_attr.attr, - &sensor_dev_attr_in6_input.dev_attr.attr, - &sensor_dev_attr_in7_input.dev_attr.attr, +static const struct hwmon_channel_info * const ads7871_info[] =3D { + HWMON_CHANNEL_INFO(in, + HWMON_I_INPUT, HWMON_I_INPUT, HWMON_I_INPUT, HWMON_I_INPUT, + HWMON_I_INPUT, HWMON_I_INPUT, HWMON_I_INPUT, HWMON_I_INPUT), NULL }; =20 -ATTRIBUTE_GROUPS(ads7871); +static const struct hwmon_ops ads7871_hwmon_ops =3D { + .is_visible =3D ads7871_is_visible, + .read =3D ads7871_read, +}; 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([116.72.73.183]) by smtp.gmail.com with ESMTPSA id d2e1a72fcca58-835158a8432sm1014523b3a.20.2026.04.30.18.30.59 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Thu, 30 Apr 2026 18:31:02 -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 Subject: [PATCH v4 3/3] hwmon: (ads7871) Use DMA-safe buffer for SPI writes Date: Fri, 1 May 2026 07:00:43 +0530 Message-ID: <20260501013044.22756-4-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: quoted-printable Content-Type: text/plain; charset="utf-8" The driver currently passes a stack-allocated buffer to spi_write(), which is incompatible with DMA on systems with CONFIG_VMAP_STACK enabled. Move the transfer buffer into the driver's private data structure to ensure it is DMA-safe. Since this shared buffer now requires serialization, this change depends on the previous commit which migrated the driver to the hwmon 'with_info' API. While moving the logic, also: - Corrected the sign extension for 14-bit data by casting to s16. - Scaled the output to millivolts (2500mV full scale ) to comply with the hwmon ABI. Signed-off-by: Tabrez Ahmed --- drivers/hwmon/ads7871.c | 37 ++++++++++++++++++++++--------------- 1 file changed, 22 insertions(+), 15 deletions(-) diff --git a/drivers/hwmon/ads7871.c b/drivers/hwmon/ads7871.c index 3ee04719eefd9..01bd5c9ad841a 100644 --- a/drivers/hwmon/ads7871.c +++ b/drivers/hwmon/ads7871.c @@ -58,12 +58,13 @@ #include #include #include -#include +#include =20 #define DEVICE_NAME "ads7871" =20 struct ads7871_data { struct spi_device *spi; + u8 tx_buf[2] ____cacheline_aligned; }; =20 static umode_t ads7871_is_visible(const void *data, @@ -100,11 +101,12 @@ static int ads7871_read_reg16(struct spi_device *spi,= int reg) return get_unaligned_le16(rx_buf); } =20 -static int ads7871_write_reg8(struct spi_device *spi, int reg, u8 val) +static int ads7871_write_reg8(struct ads7871_data *pdata, int reg, u8 val) { - u8 tmp[2] =3D {reg, val}; + pdata->tx_buf[0] =3D reg; + pdata->tx_buf[1] =3D val; =20 - return spi_write(spi, tmp, sizeof(tmp)); + return spi_write(pdata->spi, pdata->tx_buf, 2); } =20 static int ads7871_read(struct device *dev, enum hwmon_sensor_types type, @@ -123,7 +125,7 @@ static int ads7871_read(struct device *dev, enum hwmon_= sensor_types type, */ /*MUX_M3_BM forces single ended*/ /*This is also where the gain of the PGA would be set*/ - ret =3D ads7871_write_reg8(spi, REG_GAIN_MUX, + ret =3D ads7871_write_reg8(pdata, REG_GAIN_MUX, (MUX_CNV_BM | MUX_M3_BM | channel)); if (ret < 0) return ret; @@ -131,6 +133,7 @@ static int ads7871_read(struct device *dev, enum hwmon_= sensor_types type, ret =3D ads7871_read_reg8(spi, REG_GAIN_MUX); if (ret < 0) return ret; + mux_cnv =3D ((ret & MUX_CNV_BM) >> MUX_CNV_BV); /* * on 400MHz arm9 platform the conversion @@ -150,8 +153,11 @@ static int ads7871_read(struct device *dev, enum hwmon= _sensor_types type, if (raw_val < 0) return raw_val; =20 - /*result in volts*10000 =3D (val/8192)*2.5*10000*/ - *val =3D ((raw_val >> 2) * 25000) / 8192; + /* + * Use (s16) to ensure the sign bit is preserved during the shift. + * Report millivolts (2.5V =3D 2500mV). + */ + *val =3D ((s16)raw_val >> 2) * 2500 / 8192; return 0; } =20 @@ -188,11 +194,17 @@ static int ads7871_probe(struct spi_device *spi) spi->bits_per_word =3D 8; spi_setup(spi); =20 - ads7871_write_reg8(spi, REG_SER_CONTROL, 0); - ads7871_write_reg8(spi, REG_AD_CONTROL, 0); + pdata =3D devm_kzalloc(dev, sizeof(*pdata), GFP_KERNEL); + if (!pdata) + return -ENOMEM; + + pdata->spi =3D spi; + + ads7871_write_reg8(pdata, REG_SER_CONTROL, 0); + ads7871_write_reg8(pdata, REG_AD_CONTROL, 0); =20 val =3D (OSC_OSCR_BM | OSC_OSCE_BM | OSC_REFE_BM | OSC_BUFE_BM); - ads7871_write_reg8(spi, REG_OSC_CONTROL, val); + ads7871_write_reg8(pdata, REG_OSC_CONTROL, val); ret =3D ads7871_read_reg8(spi, REG_OSC_CONTROL); =20 dev_dbg(dev, "REG_OSC_CONTROL write:%x, read:%x\n", val, ret); @@ -203,11 +215,6 @@ static int ads7871_probe(struct spi_device *spi) if (val !=3D ret) return -ENODEV; =20 - pdata =3D devm_kzalloc(dev, sizeof(struct ads7871_data), GFP_KERNEL); - if (!pdata) - return -ENOMEM; - - pdata->spi =3D spi; hwmon_dev =3D devm_hwmon_device_register_with_info(dev, spi->modalias, pdata, &ads7871_chip_info, --=20 2.43.0