* [PATCH 3/3] hwmon: (pmbus/fs1412) Add TDK FS1412 driver
2026-10-09 0:56 [PATCH 0/3] hwmon: (pmbus/fs1412) Add TDK FS1412 support Abdurrahman Hussain
2026-10-09 0:56 ` [PATCH 1/3] dt-bindings: vendor-prefixes: Add TDK Corporation Abdurrahman Hussain
2026-10-09 0:56 ` [PATCH 2/3] dt-bindings: trivial-devices: Add TDK FS1412 Abdurrahman Hussain
@ 2026-10-09 0:56 ` Abdurrahman Hussain
2026-10-09 1:02 ` sashiko-bot
2 siblings, 1 reply; 9+ messages in thread
From: Abdurrahman Hussain @ 2026-10-09 0:56 UTC (permalink / raw)
To: Rob Herring, Krzysztof Kozlowski, Conor Dooley,
Abdurrahman Hussain, Guenter Roeck, Jonathan Corbet, Shuah Khan,
Randy Dunlap
Cc: devicetree, linux-kernel, linux-hwmon, linux-doc
The TDK FS1412 is a 12A uPOL regulator with PMBus telemetry for input
voltage, output voltage and temperature, plus the matching status
registers. It has over-current and over-temperature protection with
programmable fault limits but no current telemetry: READ_IOUT is not in
its command table. Its MFR_ID reads "KDT", which the driver checks
before binding.
VOUT_MODE reads 0x98: LINEAR mode with exponent -8 and bit 7 set. The
datasheet defines the output voltage limits relative to the output
voltage with a resolution of 1/256, so 0x0133 against a 0.6V command is
a 120% over-voltage limit. The PMBus core takes bits [7:5] as the mode
and rejects the device, so the driver reports VOUT_MODE with bit 7
cleared and converts the four VOUT limits to and from absolute voltages
against VOUT_COMMAND.
OT_WARN_LIMIT is not in the command table either. The register answers,
but the part has no warning threshold and reports OT_WARNING at room
temperature, so the driver hides the register from the core and only
the OT_FAULT_LIMIT based attributes are provided.
READ_VOUT reports the voltage at the feedback pin, so boards that set
the output with a resistor divider scale in2_input in user space.
Signed-off-by: Abdurrahman Hussain <abdurrahman@nexthop.ai>
---
Documentation/hwmon/fs1412.rst | 87 ++++++++++++++++++++
Documentation/hwmon/index.rst | 1 +
MAINTAINERS | 7 ++
drivers/hwmon/pmbus/Kconfig | 9 +++
drivers/hwmon/pmbus/Makefile | 1 +
drivers/hwmon/pmbus/fs1412.c | 179 +++++++++++++++++++++++++++++++++++++++++
6 files changed, 284 insertions(+)
diff --git a/Documentation/hwmon/fs1412.rst b/Documentation/hwmon/fs1412.rst
new file mode 100644
index 000000000000..b9b12fcbc5d9
--- /dev/null
+++ b/Documentation/hwmon/fs1412.rst
@@ -0,0 +1,87 @@
+.. SPDX-License-Identifier: GPL-2.0-or-later
+
+Kernel driver fs1412
+====================
+
+Supported chips:
+
+ * TDK FS1412
+
+ Prefix: 'fs1412'
+
+ Addresses scanned: -
+
+ Datasheet: https://product.tdk.com/system/files/dam/doc/product/power/switching-power/micro-pol/data_sheet/fs1412_datasheet.pdf
+
+Authors:
+ Abdurrahman Hussain <abdurrahman@nexthop.ai>
+
+
+Description
+-----------
+
+This driver implements support for the TDK FS1412, a 12A uPOL DC/DC
+regulator with PMBus monitoring of its input voltage, output voltage and
+temperature. The part has over-current and over-temperature protection with
+programmable fault limits but no current telemetry, so no current attributes
+are provided.
+
+The device answers on two I2C addresses: a register interface at the I2C
+base address (0x08 by default) and the PMBus interface at the PMBus base
+address (0x70 by default), each plus the offset strapped on the ADDR pin.
+This driver binds to the PMBus address.
+
+The driver is a client driver to the core PMBus driver.
+Please see Documentation/hwmon/pmbus.rst for details on PMBus client drivers.
+
+
+Usage Notes
+-----------
+
+This driver does not auto-detect devices. You will have to instantiate the
+devices explicitly. Please see Documentation/i2c/instantiating-devices.rst for
+details.
+
+READ_VOUT reports the voltage at the feedback (VFB) pin, not the regulated
+output. When the output is set with an external resistor divider, scale
+in2_input and the in2 limits by the divider ratio in user space.
+
+The device stores its output voltage limits relative to VOUT_COMMAND
+(VOUT_MODE bit 7 set). The driver converts them to and from absolute
+voltages, so the in2 limits read and write in the same units as in2_input.
+A written limit is stored as a 1/256 fraction of VOUT_COMMAND, so it may
+read back rounded to that resolution. The over-voltage protection itself
+engages at one of four thresholds the device rounds the fault limit to; see
+the datasheet.
+
+The part reports an over-temperature warning at room temperature and has no
+OT_WARN_LIMIT in its command table, so temp1_max and its alarm are not
+provided; temp1_crit comes from OT_FAULT_LIMIT.
+
+
+Sysfs entries
+-------------
+
+======================= ======================================================
+in1_label "vin"
+in1_input Measured input voltage
+in1_min Minimum input voltage
+in1_min_alarm Input voltage low alarm
+in1_crit Critical high input voltage
+in1_crit_alarm Input voltage critical high alarm
+
+in2_label "vout1"
+in2_input Measured voltage at the feedback pin
+in2_min Minimum output voltage
+in2_min_alarm Output voltage low alarm
+in2_max Maximum output voltage
+in2_max_alarm Output voltage high alarm
+in2_lcrit Critical low output voltage
+in2_lcrit_alarm Output voltage critical low alarm
+in2_crit Critical high output voltage
+in2_crit_alarm Output voltage critical high alarm
+
+temp1_input Measured temperature
+temp1_crit Critical high temperature
+temp1_crit_alarm Temperature critical high alarm
+======================= ======================================================
diff --git a/Documentation/hwmon/index.rst b/Documentation/hwmon/index.rst
index 9955a525436a..625833374c94 100644
--- a/Documentation/hwmon/index.rst
+++ b/Documentation/hwmon/index.rst
@@ -79,6 +79,7 @@ Hardware Monitoring Kernel Drivers
f71805f
f71882fg
fam15h_power
+ fs1412
fsp-3y
ftsteutates
g760a
diff --git a/MAINTAINERS b/MAINTAINERS
index 65e8a4b5c90b..05461a380bf7 100644
--- a/MAINTAINERS
+++ b/MAINTAINERS
@@ -26778,6 +26778,13 @@ W: https://linuxtv.org
T: git git://linuxtv.org/media.git
F: drivers/media/i2c/tda9840*
+TDK FS1412 MICRO POL DRIVER
+M: Abdurrahman Hussain <abdurrahman@nexthop.ai>
+L: linux-hwmon@vger.kernel.org
+S: Maintained
+F: Documentation/hwmon/fs1412.rst
+F: drivers/hwmon/pmbus/fs1412.c
+
TEA5761 TUNER DRIVER
M: Mauro Carvalho Chehab <mchehab@kernel.org>
L: linux-media@vger.kernel.org
diff --git a/drivers/hwmon/pmbus/Kconfig b/drivers/hwmon/pmbus/Kconfig
index eb71a0ac044b..030ef72415fe 100644
--- a/drivers/hwmon/pmbus/Kconfig
+++ b/drivers/hwmon/pmbus/Kconfig
@@ -132,6 +132,15 @@ config SENSORS_DELTA_AHE50DC_FAN
This driver can also be built as a module. If so, the module
will be called delta-ahe50dc-fan.
+config SENSORS_FS1412
+ tristate "TDK FS1412"
+ help
+ If you say yes here you get hardware monitoring support for the TDK
+ FS1412 uPOL regulator.
+
+ This driver can also be built as a module. If so, the module will
+ be called fs1412.
+
config SENSORS_FSP_3Y
tristate "FSP/3Y-Power power supplies"
help
diff --git a/drivers/hwmon/pmbus/Makefile b/drivers/hwmon/pmbus/Makefile
index e288fe72a437..7bbc0d02bfad 100644
--- a/drivers/hwmon/pmbus/Makefile
+++ b/drivers/hwmon/pmbus/Makefile
@@ -13,6 +13,7 @@ obj-$(CONFIG_SENSORS_APS_379) += aps-379.o
obj-$(CONFIG_SENSORS_BEL_PFE) += bel-pfe.o
obj-$(CONFIG_SENSORS_BPA_RS600) += bpa-rs600.o
obj-$(CONFIG_SENSORS_DELTA_AHE50DC_FAN) += delta-ahe50dc-fan.o
+obj-$(CONFIG_SENSORS_FS1412) += fs1412.o
obj-$(CONFIG_SENSORS_FSP_3Y) += fsp-3y.o
obj-$(CONFIG_SENSORS_HAC300S) += hac300s.o
obj-$(CONFIG_SENSORS_IBM_CFFPS) += ibm-cffps.o
diff --git a/drivers/hwmon/pmbus/fs1412.c b/drivers/hwmon/pmbus/fs1412.c
new file mode 100644
index 000000000000..90a72b23967e
--- /dev/null
+++ b/drivers/hwmon/pmbus/fs1412.c
@@ -0,0 +1,179 @@
+// SPDX-License-Identifier: GPL-2.0-or-later
+/*
+ * Hardware monitoring driver for the TDK FS1412 uPOL regulator
+ *
+ * Copyright 2026 Nexthop Systems.
+ */
+
+#include <linux/bits.h>
+#include <linux/i2c.h>
+#include <linux/math.h>
+#include <linux/minmax.h>
+#include <linux/module.h>
+#include <linux/of.h>
+#include <linux/pmbus.h>
+#include <linux/string.h>
+
+#include "pmbus.h"
+
+#define FS1412_MFR_ID "KDT"
+#define FS1412_MFR_ID_LEN (sizeof(FS1412_MFR_ID) - 1)
+
+/* VOUT_MODE: bit 7 selects relative VOUT limits, bits [4:0] the exponent. */
+#define FS1412_VOUT_MODE_RELATIVE BIT(7)
+#define FS1412_VOUT_MODE_EXP_MASK 0x1f
+#define FS1412_VOUT_EXP_SHIFT 8 /* exponent -8: 1/256 V per LSB */
+
+/*
+ * VOUT_MODE reads 0x98: LINEAR mode with exponent -8 and bit 7 set, which
+ * makes the VOUT limit commands relative to VOUT_COMMAND. The PMBus core
+ * treats bits [7:5] as the mode, so report the mode and exponent with bit
+ * 7 cleared and convert the relative limits in the word accessors below.
+ */
+static int fs1412_read_byte_data(struct i2c_client *client, int page, int reg)
+{
+ int ret;
+
+ if (reg != PMBUS_VOUT_MODE)
+ return -ENODATA;
+
+ ret = pmbus_read_byte_data(client, page, reg);
+ if (ret < 0 || ret == 0xff)
+ return ret;
+
+ return ret & ~FS1412_VOUT_MODE_RELATIVE;
+}
+
+static bool fs1412_vout_limit(int reg)
+{
+ switch (reg) {
+ case PMBUS_VOUT_OV_FAULT_LIMIT:
+ case PMBUS_VOUT_OV_WARN_LIMIT:
+ case PMBUS_VOUT_UV_WARN_LIMIT:
+ case PMBUS_VOUT_UV_FAULT_LIMIT:
+ return true;
+ default:
+ return false;
+ }
+}
+
+/*
+ * The VOUT limits hold the limit as a fraction of VOUT_COMMAND in the same
+ * 1/256 units, so 0x0133 on a 0.6 V command is a 120% limit. Report them
+ * as absolute voltages: limit = fraction * VOUT_COMMAND.
+ */
+static int fs1412_read_word_data(struct i2c_client *client, int page,
+ int phase, int reg)
+{
+ int rel, cmd;
+
+ /*
+ * OT_WARN_LIMIT is not in the command table. The register answers,
+ * but the part has no warning threshold and reports OT_WARNING at
+ * room temperature, so keep the core from exposing either.
+ */
+ if (reg == PMBUS_OT_WARN_LIMIT)
+ return -ENXIO;
+ if (!fs1412_vout_limit(reg))
+ return -ENODATA;
+
+ rel = pmbus_read_word_data(client, page, phase, reg);
+ if (rel < 0)
+ return rel;
+
+ cmd = pmbus_read_word_data(client, page, 0xff, PMBUS_VOUT_COMMAND);
+ if (cmd < 0)
+ return cmd;
+
+ return min_t(u32, DIV_ROUND_CLOSEST((u32)rel * cmd,
+ 1 << FS1412_VOUT_EXP_SHIFT), 0xffff);
+}
+
+static int fs1412_write_word_data(struct i2c_client *client, int page,
+ int reg, u16 word)
+{
+ int cmd;
+
+ if (reg == PMBUS_OT_WARN_LIMIT)
+ return -ENXIO;
+ if (!fs1412_vout_limit(reg))
+ return -ENODATA;
+
+ cmd = pmbus_read_word_data(client, page, 0xff, PMBUS_VOUT_COMMAND);
+ if (cmd < 0)
+ return cmd;
+ if (!cmd)
+ return -EINVAL;
+
+ word = clamp_val(DIV_ROUND_CLOSEST(word << FS1412_VOUT_EXP_SHIFT, cmd),
+ 0, 0xffff);
+
+ return pmbus_write_word_data(client, page, reg, word);
+}
+
+static struct pmbus_driver_info fs1412_info = {
+ .pages = 1,
+ .format[PSC_VOLTAGE_IN] = linear,
+ .format[PSC_VOLTAGE_OUT] = linear,
+ .format[PSC_TEMPERATURE] = linear,
+ .func[0] = PMBUS_HAVE_VIN | PMBUS_HAVE_STATUS_INPUT |
+ PMBUS_HAVE_VOUT | PMBUS_HAVE_STATUS_VOUT |
+ PMBUS_HAVE_TEMP | PMBUS_HAVE_STATUS_TEMP,
+ .read_byte_data = fs1412_read_byte_data,
+ .read_word_data = fs1412_read_word_data,
+ .write_word_data = fs1412_write_word_data,
+};
+
+static int fs1412_probe(struct i2c_client *client)
+{
+ char buf[I2C_SMBUS_BLOCK_MAX + 1] = { 0 };
+ struct device *dev = &client->dev;
+ int ret;
+
+ ret = i2c_smbus_read_block_data(client, PMBUS_MFR_ID, buf);
+ if (ret < 0)
+ return dev_err_probe(dev, ret, "Failed to read PMBUS_MFR_ID\n");
+
+ if (ret != FS1412_MFR_ID_LEN ||
+ strncmp(buf, FS1412_MFR_ID, FS1412_MFR_ID_LEN))
+ return dev_err_probe(dev, -ENODEV,
+ "Unsupported Manufacturer ID '%s'\n", buf);
+
+ /* The relative limit conversion assumes the 1/256 V exponent. */
+ ret = i2c_smbus_read_byte_data(client, PMBUS_VOUT_MODE);
+ if (ret < 0)
+ return dev_err_probe(dev, ret, "Failed to read VOUT_MODE\n");
+ if ((ret & FS1412_VOUT_MODE_EXP_MASK) != 0x18)
+ return dev_err_probe(dev, -ENODEV,
+ "Unsupported VOUT_MODE 0x%02x\n", ret);
+
+ return pmbus_do_probe(client, &fs1412_info);
+}
+
+static const struct i2c_device_id fs1412_id[] = {
+ { .name = "fs1412" },
+ { }
+};
+MODULE_DEVICE_TABLE(i2c, fs1412_id);
+
+static const struct of_device_id fs1412_of_match[] = {
+ { .compatible = "tdk,fs1412" },
+ { }
+};
+MODULE_DEVICE_TABLE(of, fs1412_of_match);
+
+static struct i2c_driver fs1412_driver = {
+ .driver = {
+ .name = "fs1412",
+ .of_match_table = fs1412_of_match,
+ },
+ .probe = fs1412_probe,
+ .id_table = fs1412_id,
+};
+
+module_i2c_driver(fs1412_driver);
+
+MODULE_AUTHOR("Abdurrahman Hussain <abdurrahman@nexthop.ai>");
+MODULE_DESCRIPTION("PMBus driver for the TDK FS1412 uPOL regulator");
+MODULE_LICENSE("GPL");
+MODULE_IMPORT_NS("PMBUS");
--
2.54.0
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