[PATCH v2] hwmon: add a driver for the temp/voltage sensor on PolarFire SoC

[PATCH v2] hwmon: add a driver for the temp/voltage sensor on PolarFire SoC

[Conor Dooley]

From: Lars Randers <lranders@mail.dk>

Add a driver for the temperature and voltage sensors on PolarFire SoC.
The temperature reports how hot the die is, and the voltages are the
SoC's 1.05, 1.8 and 2.5 volt rails respectively.

The hardware supports alarms in theory, but there is an erratum that
prevents clearing them once triggered, so no support is added for them.

The hardware measures voltage with 16 bits, of which 1 is a sign bit and
the remainder holds the voltage as a fixed point integer value. It's
improbable that the hardware will work if the voltages are negative, so
the driver ignores the sign bits.

There's no dt support etc here because this is the child of a simple-mfd
syscon.

Signed-off-by: Lars Randers <lranders@mail.dk>
Co-developed-by: Conor Dooley <conor.dooley@microchip.com>
Signed-off-by: Conor Dooley <conor.dooley@microchip.com>
---

v2:
- Fix some minor things pointed out by Sashiko including inaccurate
  comments, bounds checking of values read from sysfs and Kconfig
  dependencies.
- Make update_interval use milliseconds instead of microseconds
  (I'll add update_interval_us support when that lands, there's a
  proposed workaround for the erratum circulating internally, so it'll
  probably come alongside alarm support).

CC: Guenter Roeck <linux@roeck-us.net>
CC: Jonathan Corbet <corbet@lwn.net>
CC: Shuah Khan <skhan@linuxfoundation.org>
CC: Conor Dooley <conor.dooley@microchip.com>
CC: Daire McNamara <daire.mcnamara@microchip.com>
CC: linux-hwmon@vger.kernel.org
CC: linux-doc@vger.kernel.org
CC: linux-kernel@vger.kernel.org
CC: linux-riscv@lists.infradead.org
CC: Valentina.FernandezAlanis@microchip.com
---
 Documentation/hwmon/index.rst    |   1 +
 Documentation/hwmon/tvs-mpfs.rst |  53 +++++
 MAINTAINERS                      |   1 +
 drivers/hwmon/Kconfig            |  13 +
 drivers/hwmon/Makefile           |   1 +
 drivers/hwmon/tvs-mpfs.c         | 394 +++++++++++++++++++++++++++++++
 6 files changed, 463 insertions(+)
 create mode 100644 Documentation/hwmon/tvs-mpfs.rst
 create mode 100644 drivers/hwmon/tvs-mpfs.c

diff --git a/Documentation/hwmon/index.rst b/Documentation/hwmon/index.rst
index 8b655e5d6b68..84a5339e1d6f 100644
--- a/Documentation/hwmon/index.rst
+++ b/Documentation/hwmon/index.rst
@@ -262,6 +262,7 @@ Hardware Monitoring Kernel Drivers
    tps53679
    tps546d24
    tsc1641
+   tvs-mpfs
    twl4030-madc-hwmon
    ucd9000
    ucd9200
diff --git a/Documentation/hwmon/tvs-mpfs.rst b/Documentation/hwmon/tvs-mpfs.rst
new file mode 100644
index 000000000000..ff445844d07c
--- /dev/null
+++ b/Documentation/hwmon/tvs-mpfs.rst
@@ -0,0 +1,53 @@
+.. SPDX-License-Identifier: GPL-2.0
+
+Kernel driver tvs-mpfs
+======================
+
+Supported chips:
+
+  * PolarFire SoC
+
+Authors:
+
+   - Conor Dooley <conor.dooley@microchip.com>
+   - Lars Randers <lranders@mail.dk>
+
+Description
+-----------
+
+This driver implements support for the temperature and voltage sensors on
+PolarFire SoC. The temperature reports how hot the die is, and the voltages are
+the SoC's 1.05, 1.8 and 2.5 volt rails respectively.
+
+
+Usage Notes
+-----------
+
+update_interval has a permitted range of 0 to 8.
+
+Temperatures are read in millidegrees Celsius, but the hardware measures in
+degrees Kelvin, storing the result as 11.4 fixed point data, for a maximum
+value of 2047.9375 degrees Kelvin.
+
+Voltages are read in millivolts. The hardware measures in millivolts, storing
+the value as 12.3 fixed point data, for a maximum of 4095.875 millivolts.
+The minimum value reportable by the driver is 0 volts, although the hardware
+is capable of measuring negative values.
+
+Sysfs entries
+-------------
+
+The following attributes are supported. update_interval is read-write, as are
+the enables. All other attributes are read only.
+
+======================= ====================================================
+temp1_label		Fixed name for channel.
+temp1_input		Measured temperature for channel.
+temp1_enable		Enable/disable for channel.
+
+in[0-2]_label		Fixed name for channel.
+in[0-2]_input		Measured voltage for channel.
+in[0-2]_enable		Enable/disable for channel.
+
+update_interval		The interval at which the chip will update readings.
+======================= ====================================================
diff --git a/MAINTAINERS b/MAINTAINERS
index 2fb1c75afd16..a492cf5ad0fc 100644
--- a/MAINTAINERS
+++ b/MAINTAINERS
@@ -22938,6 +22938,7 @@ F:	drivers/char/hw_random/mpfs-rng.c
 F:	drivers/clk/microchip/clk-mpfs*.c
 F:	drivers/firmware/microchip/mpfs-auto-update.c
 F:	drivers/gpio/gpio-mpfs.c
+F:	drivers/hwmon/tvs-mpfs.c
 F:	drivers/i2c/busses/i2c-microchip-corei2c.c
 F:	drivers/mailbox/mailbox-mpfs.c
 F:	drivers/pci/controller/plda/pcie-microchip-host.c
diff --git a/drivers/hwmon/Kconfig b/drivers/hwmon/Kconfig
index 14e4cea48acc..2b9622b1db95 100644
--- a/drivers/hwmon/Kconfig
+++ b/drivers/hwmon/Kconfig
@@ -930,6 +930,19 @@ config SENSORS_JC42
 	  This driver can also be built as a module. If so, the module
 	  will be called jc42.
 
+config SENSORS_POLARFIRE_SOC_TVS
+	tristate "PolarFire SoC (MPFS) temperature and voltage sensor"
+	depends on POLARFIRE_SOC_SYSCONS || COMPILE_TEST
+	depends on MFD_SYSCON
+	help
+	  This driver adds support for the PolarFire SoC (MPFS) Temperature and
+	  Voltage Sensor.
+
+	  To compile this driver as a module, choose M here. the
+	  module will be called tvs-mpfs.
+
+	  If unsure, say N.
+
 config SENSORS_POWERZ
 	tristate "ChargerLAB POWER-Z USB-C tester"
 	depends on USB
diff --git a/drivers/hwmon/Makefile b/drivers/hwmon/Makefile
index 4788996aa137..b58d249e4cf4 100644
--- a/drivers/hwmon/Makefile
+++ b/drivers/hwmon/Makefile
@@ -194,6 +194,7 @@ obj-$(CONFIG_SENSORS_NZXT_SMART2) += nzxt-smart2.o
 obj-$(CONFIG_SENSORS_PC87360)	+= pc87360.o
 obj-$(CONFIG_SENSORS_PC87427)	+= pc87427.o
 obj-$(CONFIG_SENSORS_PCF8591)	+= pcf8591.o
+obj-$(CONFIG_SENSORS_POLARFIRE_SOC_TVS)  += tvs-mpfs.o
 obj-$(CONFIG_SENSORS_POWERZ)	+= powerz.o
 obj-$(CONFIG_SENSORS_POWR1220)  += powr1220.o
 obj-$(CONFIG_SENSORS_PT5161L)	+= pt5161l.o
diff --git a/drivers/hwmon/tvs-mpfs.c b/drivers/hwmon/tvs-mpfs.c
new file mode 100644
index 000000000000..f086f178b4ba
--- /dev/null
+++ b/drivers/hwmon/tvs-mpfs.c
@@ -0,0 +1,394 @@
+// SPDX-License-Identifier: GPL-2.0+
+/*
+ * Author: Lars Randers <lranders@mail.dk>
+ */
+
+#include <linux/bitfield.h>
+#include <linux/err.h>
+#include <linux/freezer.h>
+#include <linux/hwmon.h>
+#include <linux/io.h>
+#include <linux/kthread.h>
+#include <linux/mfd/syscon.h>
+#include <linux/module.h>
+#include <linux/of_address.h>
+#include <linux/platform_device.h>
+#include <linux/regmap.h>
+
+#define MPFS_TVS_CTRL 0x08
+#define MPFS_TVS_OUTPUT0 0x24
+#define MPFS_TVS_OUTPUT1 0x28
+
+#define MPFS_TVS_CTRL_TEMP_VALID	BIT(19)
+#define MPFS_TVS_CTRL_V2P5_VALID	BIT(18)
+#define MPFS_TVS_CTRL_V1P8_VALID	BIT(17)
+#define MPFS_TVS_CTRL_V1P05_VALID	BIT(16)
+
+#define MPFS_TVS_CTRL_TEMP_ENABLE	BIT(3)
+#define MPFS_TVS_CTRL_V2P5_ENABLE	BIT(2)
+#define MPFS_TVS_CTRL_V1P8_ENABLE	BIT(1)
+#define MPFS_TVS_CTRL_V1P05_ENABLE	BIT(0)
+#define MPFS_TVS_CTRL_ENABLE_ALL	GENMASK(3, 0)
+
+/*
+ * For all of these the value in millivolts is stored in 16 bits, with an upper
+ * sign bit and a lower 3 bits of decimal. These masks discard the sign bit and
+ * decimal places, because if Linux is running these voltages cannot be negative
+ * and so avoid having to convert to two's complement.
+ */
+#define MPFS_OUTPUT0_V1P8_MASK	GENMASK(30, 19)
+#define MPFS_OUTPUT0_V1P05_MASK	GENMASK(14, 3)
+#define MPFS_OUTPUT1_V2P5_MASK	GENMASK(14, 3)
+
+/*
+ * The register map claims that the temperature is stored in bits 31:16, but
+ * application note "AN4682: PolarFire FPGA Temperature and Voltage Sensor"
+ * says that 31 is reserved. Temperature is in kelvin, so what's probably a
+ * sign bit has no value anyway.
+ */
+#define MPFS_OUTPUT1_TEMP_MASK GENMASK(30, 16)
+
+#define MPFS_TVS_INTERVAL_MASK GENMASK(15, 8)
+#define MPFS_TVS_INTERVAL_OFFSET 8
+/* The interval register is in increments of 32 us */
+#define MPFS_TVS_INTERVAL_SCALE 32
+
+/* 273.1875 in 11.4 fixed-point notation */
+#define MPFS_TVS_K_TO_C 0x1113
+
+enum mpfs_tvs_sensors {
+	SENSOR_V1P05 = 0,
+	SENSOR_V1P8,
+	SENSOR_V2P5,
+};
+
+static const char * const mpfs_tvs_voltage_labels[] = { "1P05", "1P8", "2P5" };
+
+struct mpfs_tvs {
+	struct regmap *regmap;
+};
+
+static int mpfs_tvs_voltage_read(struct mpfs_tvs *data, u32 attr,
+				 int channel, long *val)
+{
+	u32 tmp, control;
+
+	if (attr != hwmon_in_input && attr != hwmon_in_enable)
+		return -EOPNOTSUPP;
+
+	regmap_read(data->regmap, MPFS_TVS_CTRL, &control);
+
+	switch (channel) {
+	case SENSOR_V2P5:
+		if (attr == hwmon_in_enable) {
+			*val = FIELD_GET(MPFS_TVS_CTRL_V2P5_ENABLE, control);
+			break;
+		}
+
+		if (!(control & MPFS_TVS_CTRL_V2P5_VALID))
+			return -EINVAL;
+
+		regmap_read(data->regmap, MPFS_TVS_OUTPUT1, &tmp);
+		*val = FIELD_GET(MPFS_OUTPUT1_V2P5_MASK, tmp);
+		break;
+	case SENSOR_V1P8:
+		if (attr == hwmon_in_enable) {
+			*val = FIELD_GET(MPFS_TVS_CTRL_V1P8_ENABLE, control);
+			break;
+		}
+
+		if (!(control & MPFS_TVS_CTRL_V1P8_VALID))
+			return -EINVAL;
+
+		regmap_read(data->regmap, MPFS_TVS_OUTPUT0, &tmp);
+		*val = FIELD_GET(MPFS_OUTPUT0_V1P8_MASK, tmp);
+		break;
+	case SENSOR_V1P05:
+		if (attr == hwmon_in_enable) {
+			*val = FIELD_GET(MPFS_TVS_CTRL_V1P05_ENABLE, control);
+			break;
+		}
+
+		if (!(control & MPFS_TVS_CTRL_V1P05_VALID))
+			return -EINVAL;
+
+		regmap_read(data->regmap, MPFS_TVS_OUTPUT0, &tmp);
+		*val = FIELD_GET(MPFS_OUTPUT0_V1P05_MASK, tmp);
+		break;
+	default:
+		return -EOPNOTSUPP;
+	}
+
+	return 0;
+}
+
+static int mpfs_tvs_voltage_write(struct mpfs_tvs *data, u32 attr,
+				  int channel, long val)
+{
+	u32 tmp;
+
+	if (attr != hwmon_in_enable)
+		return -EOPNOTSUPP;
+
+	switch (channel) {
+	case SENSOR_V2P5:
+		if (val > 1 || val < 0)
+			return -EINVAL;
+
+		tmp = FIELD_PREP(MPFS_TVS_CTRL_V2P5_ENABLE, val);
+		regmap_update_bits(data->regmap, MPFS_TVS_CTRL,
+				   MPFS_TVS_CTRL_V2P5_ENABLE, tmp);
+		break;
+	case SENSOR_V1P8:
+		if (val > 1 || val < 0)
+			return -EINVAL;
+
+		tmp = FIELD_PREP(MPFS_TVS_CTRL_V1P8_ENABLE, val);
+		regmap_update_bits(data->regmap, MPFS_TVS_CTRL,
+				   MPFS_TVS_CTRL_V1P8_ENABLE, tmp);
+		break;
+	case SENSOR_V1P05:
+		if (val > 1 || val < 0)
+			return -EINVAL;
+
+		tmp = FIELD_PREP(MPFS_TVS_CTRL_V1P05_ENABLE, val);
+		regmap_update_bits(data->regmap, MPFS_TVS_CTRL,
+				   MPFS_TVS_CTRL_V1P05_ENABLE, tmp);
+		break;
+	default:
+		return -EOPNOTSUPP;
+	}
+
+	return 0;
+}
+
+static int mpfs_tvs_temp_read(struct mpfs_tvs *data, u32 attr, long *val)
+{
+	u32 tmp, control;
+
+	if (attr != hwmon_temp_input && attr != hwmon_temp_enable)
+		return -EOPNOTSUPP;
+
+	regmap_read(data->regmap, MPFS_TVS_CTRL, &control);
+
+	if (attr == hwmon_temp_enable) {
+		*val = FIELD_GET(MPFS_TVS_CTRL_TEMP_ENABLE, control);
+		return 0;
+	}
+
+	if (!(control & MPFS_TVS_CTRL_TEMP_VALID))
+		return -EINVAL;
+
+	regmap_read(data->regmap, MPFS_TVS_OUTPUT1, &tmp);
+	*val = FIELD_GET(MPFS_OUTPUT1_TEMP_MASK, tmp);
+	*val -= MPFS_TVS_K_TO_C;
+	*val = (1000 * *val) >> 4; /* fixed point (11.4) to millidegrees */
+
+	return 0;
+}
+
+static int mpfs_tvs_temp_write(struct mpfs_tvs *data, u32 attr, long val)
+{
+	u32 tmp;
+
+	if (attr != hwmon_temp_enable)
+		return -EOPNOTSUPP;
+
+	if (val > 1 || val < 0)
+		return -EINVAL;
+
+	tmp = FIELD_PREP(MPFS_TVS_CTRL_TEMP_ENABLE, val);
+	regmap_update_bits(data->regmap, MPFS_TVS_CTRL,
+			   MPFS_TVS_CTRL_TEMP_ENABLE, tmp);
+
+	return 0;
+}
+
+static int mpfs_tvs_interval_read(struct mpfs_tvs *data, u32 attr, long *val)
+{
+	u32 tmp;
+
+	if (attr != hwmon_chip_update_interval)
+		return -EOPNOTSUPP;
+
+	regmap_read(data->regmap, MPFS_TVS_CTRL, &tmp);
+	*val = FIELD_GET(MPFS_TVS_INTERVAL_MASK, tmp);
+	*val *= MPFS_TVS_INTERVAL_SCALE;
+	*val /= 1000;
+
+	return 0;
+}
+
+static int mpfs_tvs_interval_write(struct mpfs_tvs *data, u32 attr, long val)
+{
+	unsigned long temp = val;
+
+	if (attr != hwmon_chip_update_interval)
+		return -EOPNOTSUPP;
+
+	temp *= 1000;
+	temp /= MPFS_TVS_INTERVAL_SCALE;
+
+	/*
+	 * The value is 8 bits wide, but 255 is described as
+	 * "255= Do single set of transfers when scoverride set"
+	 * but there's no scoverride bit in the tvs register region.
+	 * Ban using 255 since its behaviour is suspect.
+	 */
+	if (temp > 254)
+		return -EINVAL;
+
+	temp <<= MPFS_TVS_INTERVAL_OFFSET;
+	regmap_update_bits(data->regmap, MPFS_TVS_CTRL,
+			   MPFS_TVS_INTERVAL_MASK, temp);
+
+	return 0;
+}
+
+static umode_t mpfs_tvs_is_visible(const void *data,
+				   enum hwmon_sensor_types type,
+				   u32 attr, int channel)
+{
+	if (type == hwmon_chip && attr == hwmon_chip_update_interval)
+		return 0644;
+
+	if (type == hwmon_temp) {
+		switch (attr) {
+		case hwmon_temp_enable:
+			return 0644;
+		case hwmon_temp_input:
+		case hwmon_temp_label:
+			return 0444;
+		default:
+			return 0;
+		}
+	}
+
+	if (type == hwmon_in) {
+		switch (attr) {
+		case hwmon_in_enable:
+			return 0644;
+		case hwmon_in_input:
+		case hwmon_in_label:
+			return 0444;
+		default:
+			return 0;
+		}
+	}
+
+	return 0;
+}
+
+static int mpfs_tvs_read(struct device *dev, enum hwmon_sensor_types type,
+			 u32 attr, int channel, long *val)
+{
+	struct mpfs_tvs *data = dev_get_drvdata(dev);
+
+	switch (type) {
+	case hwmon_temp:
+		return mpfs_tvs_temp_read(data, attr, val);
+	case hwmon_in:
+		return mpfs_tvs_voltage_read(data, attr, channel, val);
+	case hwmon_chip:
+		return mpfs_tvs_interval_read(data, attr, val);
+	default:
+		return -EOPNOTSUPP;
+	}
+}
+
+static int mpfs_tvs_write(struct device *dev, enum hwmon_sensor_types type,
+			  u32 attr, int channel, long val)
+{
+	struct mpfs_tvs *data = dev_get_drvdata(dev);
+
+	switch (type) {
+	case hwmon_temp:
+		return mpfs_tvs_temp_write(data, attr, val);
+	case hwmon_in:
+		return mpfs_tvs_voltage_write(data, attr, channel, val);
+	case hwmon_chip:
+		return mpfs_tvs_interval_write(data, attr, val);
+	default:
+		return -EOPNOTSUPP;
+	}
+}
+
+static int mpfs_tvs_read_labels(struct device *dev,
+				enum hwmon_sensor_types type,
+				u32 attr, int channel,
+				const char **str)
+{
+	switch (type) {
+	case hwmon_temp:
+		*str = "Die Temp";
+		return 0;
+	case hwmon_in:
+		*str = mpfs_tvs_voltage_labels[channel];
+		return 0;
+	default:
+		return -EOPNOTSUPP;
+	}
+}
+
+static const struct hwmon_ops mpfs_tvs_ops = {
+	.is_visible = mpfs_tvs_is_visible,
+	.read_string = mpfs_tvs_read_labels,
+	.read = mpfs_tvs_read,
+	.write = mpfs_tvs_write,
+};
+
+static const struct hwmon_channel_info *mpfs_tvs_info[] = {
+	HWMON_CHANNEL_INFO(chip,
+			   HWMON_C_REGISTER_TZ | HWMON_C_UPDATE_INTERVAL),
+	HWMON_CHANNEL_INFO(temp,
+			   HWMON_T_INPUT | HWMON_T_LABEL | HWMON_T_ENABLE),
+	HWMON_CHANNEL_INFO(in,
+			   HWMON_I_INPUT | HWMON_I_LABEL | HWMON_I_ENABLE,
+			   HWMON_I_INPUT | HWMON_I_LABEL | HWMON_I_ENABLE,
+			   HWMON_I_INPUT | HWMON_I_LABEL | HWMON_I_ENABLE),
+	NULL
+};
+
+static const struct hwmon_chip_info mpfs_tvs_chip_info = {
+	.ops = &mpfs_tvs_ops,
+	.info = mpfs_tvs_info,
+};
+
+static int mpfs_tvs_probe(struct platform_device *pdev)
+{
+	struct device *hwmon_dev;
+	struct mpfs_tvs *data;
+
+	data = devm_kzalloc(&pdev->dev, sizeof(*data), GFP_KERNEL);
+	if (!data)
+		return -ENOMEM;
+
+	data->regmap = device_node_to_regmap(pdev->dev.parent->of_node);
+	if (IS_ERR(data->regmap))
+		return dev_err_probe(&pdev->dev, PTR_ERR(data->regmap),
+				     "Failed to find syscon regmap\n");
+
+	regmap_write(data->regmap, MPFS_TVS_CTRL, MPFS_TVS_CTRL_ENABLE_ALL);
+
+	hwmon_dev = devm_hwmon_device_register_with_info(&pdev->dev, "mpfs_tvs",
+							 data,
+							 &mpfs_tvs_chip_info,
+							 NULL);
+	if (IS_ERR(hwmon_dev))
+		return dev_err_probe(&pdev->dev, PTR_ERR(hwmon_dev),
+				     "hwmon device registration failed.\n");
+
+	return 0;
+}
+
+static struct platform_driver mpfs_tvs_driver = {
+	.probe = mpfs_tvs_probe,
+	.driver = {
+		.name = "mpfs-tvs",
+	},
+};
+module_platform_driver(mpfs_tvs_driver);
+
+MODULE_AUTHOR("Lars Randers <lranders@mail.dk>");
+MODULE_DESCRIPTION("PolarFire SoC temperature & voltage sensor driver");
+MODULE_LICENSE("GPL");
-- 
2.53.0

Re: [PATCH v2] hwmon: add a driver for the temp/voltage sensor on PolarFire SoC

[sashiko-bot]

Thank you for your contribution! Sashiko AI review found 4 potential issue(s) to consider:
- [High] Ignored `regmap_read()` return values lead to the use of uninitialized stack variables, potentially leaking kernel memory.
- [Medium] Arithmetic overflow in `mpfs_tvs_interval_write` bypasses interval bounds checking.
- [Medium] The driver ignores the return values of hardware write operations, masking errors from the hwmon core and userspace.
- [Medium] Destructive `regmap_write()` to the control register overwrites existing configuration, such as the update interval.
--

commit 3e2d5f8cc5d07efdc63c9af851354b4ce076c3a4
Author: Lars Randers <lranders@mail.dk>
Subject: hwmon: add a driver for the temp/voltage sensor on PolarFire SoC

Add a driver for the temperature and voltage sensors on PolarFire SoC.
The temperature reports how hot the die is, and the voltages are the
SoC's 1.05, 1.8 and 2.5 volt rails respectively.

> diff --git a/drivers/hwmon/tvs-mpfs.c b/drivers/hwmon/tvs-mpfs.c
> new file mode 100644
> index 0000000000000..f086f178b4bab
> --- /dev/null
> +++ b/drivers/hwmon/tvs-mpfs.c

[ ... ]

> +static int mpfs_tvs_voltage_read(struct mpfs_tvs *data, u32 attr,
> +				 int channel, long *val)
> +{
> +	u32 tmp, control;
> +
> +	if (attr != hwmon_in_input && attr != hwmon_in_enable)
> +		return -EOPNOTSUPP;
> +
> +	regmap_read(data->regmap, MPFS_TVS_CTRL, &control);
        ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^

[Severity: High]
Does this code leak uninitialized stack memory if the hardware read fails?

Because the return value of regmap_read() is ignored, control (and tmp
below) could remain uninitialized on a read failure. This uninitialized
data is then used in bitwise operations and potentially returned to
userspace via *val.

The same pattern appears in mpfs_tvs_temp_read() and mpfs_tvs_interval_read().

> +
> +	switch (channel) {
> +	case SENSOR_V2P5:

[ ... ]

> +static int mpfs_tvs_voltage_write(struct mpfs_tvs *data, u32 attr,
> +				  int channel, long val)
> +{
> +	u32 tmp;
> +
> +	if (attr != hwmon_in_enable)
> +		return -EOPNOTSUPP;
> +
> +	switch (channel) {
> +	case SENSOR_V2P5:
> +		if (val > 1 || val < 0)
> +			return -EINVAL;
> +
> +		tmp = FIELD_PREP(MPFS_TVS_CTRL_V2P5_ENABLE, val);
> +		regmap_update_bits(data->regmap, MPFS_TVS_CTRL,
> +				   MPFS_TVS_CTRL_V2P5_ENABLE, tmp);
                ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^

[Severity: Medium]
Should this check the return value of regmap_update_bits()?

By unconditionally returning 0 at the end of the function, hardware write 
failures are masked from the hwmon core and userspace.

The same pattern appears in mpfs_tvs_temp_write() and 
mpfs_tvs_interval_write().

> +		break;

[ ... ]

> +static int mpfs_tvs_interval_write(struct mpfs_tvs *data, u32 attr, long val)
> +{
> +	unsigned long temp = val;
> +
> +	if (attr != hwmon_chip_update_interval)
> +		return -EOPNOTSUPP;
> +
> +	temp *= 1000;
        ^^^^^^^^^^^^^

[Severity: Medium]
Could this multiplication overflow before bounds validation occurs?

If a large value is passed (e.g., val = 4294968 on a 32-bit architecture),
temp * 1000 could wrap around to a small value like 480. Divided by 
MPFS_TVS_INTERVAL_SCALE (32), this gives 15, which would successfully pass 
the temp > 254 upper-bound check below and silently write an invalid 
interval to the hardware.

> +	temp /= MPFS_TVS_INTERVAL_SCALE;
> +
> +	/*
> +	 * The value is 8 bits wide, but 255 is described as
> +	 * "255= Do single set of transfers when scoverride set"
> +	 * but there's no scoverride bit in the tvs register region.
> +	 * Ban using 255 since its behaviour is suspect.
> +	 */
> +	if (temp > 254)
> +		return -EINVAL;
> +
> +	temp <<= MPFS_TVS_INTERVAL_OFFSET;
> +	regmap_update_bits(data->regmap, MPFS_TVS_CTRL,
> +			   MPFS_TVS_INTERVAL_MASK, temp);
> +
> +	return 0;
> +}

[ ... ]

> +static int mpfs_tvs_probe(struct platform_device *pdev)
> +{
> +	struct device *hwmon_dev;
> +	struct mpfs_tvs *data;
> +
> +	data = devm_kzalloc(&pdev->dev, sizeof(*data), GFP_KERNEL);
> +	if (!data)
> +		return -ENOMEM;
> +
> +	data->regmap = device_node_to_regmap(pdev->dev.parent->of_node);
> +	if (IS_ERR(data->regmap))
> +		return dev_err_probe(&pdev->dev, PTR_ERR(data->regmap),
> +				     "Failed to find syscon regmap\n");
> +
> +	regmap_write(data->regmap, MPFS_TVS_CTRL, MPFS_TVS_CTRL_ENABLE_ALL);
        ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^

[Severity: Medium]
Does this destructively overwrite existing configuration in the control register?

Because this uses regmap_write() rather than a read-modify-write operation
like regmap_update_bits(), it replaces the entire register contents. This 
clears the INTERVAL bits (15:8) to 0 and zeroes out other status bits, which 
might erase configuration previously set by the bootloader.

> +
> +	hwmon_dev = devm_hwmon_device_register_with_info(&pdev->dev, "mpfs_tvs",
> +							 data,
> +							 &mpfs_tvs_chip_info,
> +							 NULL);

-- 
Sashiko AI review · https://sashiko.dev/#/patchset/20260603-ongoing-brunette-51e35be6d93e@spud?part=1