diff --git a/Documentation/hwmon/fsp-3y.rst b/Documentation/hwmon/fsp-3y.rst
new file mode 100644
index 0000000000000000000000000000000000000000..5693d83a20358cf46d526282c2a998ad066cc8a0
--- /dev/null
+++ b/Documentation/hwmon/fsp-3y.rst
@@ -0,0 +1,28 @@
+.. SPDX-License-Identifier: GPL-2.0
+
+Kernel driver fsp3y
+======================
+Supported devices:
+ * 3Y POWER YH-5151E
+ * 3Y POWER YM-2151E
+
+Author: Václav Kubernát <kubernat@cesnet.cz>
+
+Description
+-----------
+This driver implements limited support for two 3Y POWER devices.
+
+Sysfs entries
+-------------
+ * in1_input input voltage
+ * in2_input 12V output voltage
+ * in3_input 5V output voltage
+ * curr1_input input current
+ * curr2_input 12V output current
+ * curr3_input 5V output current
+ * fan1_input fan rpm
+ * temp1_input temperature 1
+ * temp2_input temperature 2
+ * temp3_input temperature 3
+ * power1_input input power
+ * power2_input output power
diff --git a/Documentation/hwmon/index.rst b/Documentation/hwmon/index.rst
index a846eff10edf1977e580d930074b19541b743608..d6a050f85477b984a408316a3c9f8d9e0dc9dbb1 100644
--- a/Documentation/hwmon/index.rst
+++ b/Documentation/hwmon/index.rst
@@ -63,6 +63,7 @@ Hardware Monitoring Kernel Drivers
f71805f
f71882fg
fam15h_power
+ fsp-3y
ftsteutates
g760a
g762
diff --git a/drivers/hwmon/pmbus/Kconfig b/drivers/hwmon/pmbus/Kconfig
index fd0911017be6112d2c9781a18c5fb72c31f1dfc5..e9727176b16703b068b90e3003ff8fbccba24e3f 100644
--- a/drivers/hwmon/pmbus/Kconfig
+++ b/drivers/hwmon/pmbus/Kconfig
@@ -65,6 +65,16 @@ config SENSORS_BPA_RS600
This driver can also be built as a module. If so, the module will
be called bpa-rs600.
+config SENSORS_FSP_3Y
+ tristate "FSP/3Y-Power power supplies"
+ help
+ If you say yes here you get hardware monitoring support for
+ FSP/3Y-Power hot-swap power supplies.
+ Supported models: YH-5151E, YM-2151E
+
+ This driver can also be built as a module. If so, the module will
+ be called fsp-3y.
+
config SENSORS_IBM_CFFPS
tristate "IBM Common Form Factor Power Supply"
depends on LEDS_CLASS
diff --git a/drivers/hwmon/pmbus/Makefile b/drivers/hwmon/pmbus/Makefile
index 2408231980ad7e8adc8d0b1ecbe632c239747b35..4ca98e9005f1304f214adc0b1c4cb29032e176b6 100644
--- a/drivers/hwmon/pmbus/Makefile
+++ b/drivers/hwmon/pmbus/Makefile
@@ -9,6 +9,7 @@ obj-$(CONFIG_SENSORS_ADM1266) += adm1266.o
obj-$(CONFIG_SENSORS_ADM1275) += adm1275.o
obj-$(CONFIG_SENSORS_BEL_PFE) += bel-pfe.o
obj-$(CONFIG_SENSORS_BPA_RS600) += bpa-rs600.o
+obj-$(CONFIG_SENSORS_FSP_3Y) += fsp-3y.o
obj-$(CONFIG_SENSORS_IBM_CFFPS) += ibm-cffps.o
obj-$(CONFIG_SENSORS_INSPUR_IPSPS) += inspur-ipsps.o
obj-$(CONFIG_SENSORS_IR35221) += ir35221.o
diff --git a/drivers/hwmon/pmbus/fsp-3y.c b/drivers/hwmon/pmbus/fsp-3y.c
new file mode 100644
index 0000000000000000000000000000000000000000..284b73aaed46700517ea8e9840ade24df23527d1
--- /dev/null
+++ b/drivers/hwmon/pmbus/fsp-3y.c
@@ -0,0 +1,253 @@
+// SPDX-License-Identifier: GPL-2.0-or-later
+/*
+ * Hardware monitoring driver for FSP 3Y-Power PSUs
+ *
+ * Copyright (c) 2021 Václav Kubernát, CESNET
+ *
+ * This driver is mostly reverse engineered with the help of a tool called pmbus_peek written by
+ * David Brownell (and later adopted by Jan Kundrát). The device has some sort of a timing issue
+ * when switching pages, details are explained in the code. The driver support is limited. It
+ * exposes only the values, that have been tested to work correctly. Unsupported values either
+ * aren't supported by the devices or their encondings are unknown.
+ */
+
+#include <linux/delay.h>
+#include <linux/i2c.h>
+#include <linux/kernel.h>
+#include <linux/module.h>
+#include "pmbus.h"
+
+#define YM2151_PAGE_12V_LOG 0x00
+#define YM2151_PAGE_12V_REAL 0x00
+#define YM2151_PAGE_5VSB_LOG 0x01
+#define YM2151_PAGE_5VSB_REAL 0x20
+#define YH5151E_PAGE_12V_LOG 0x00
+#define YH5151E_PAGE_12V_REAL 0x00
+#define YH5151E_PAGE_5V_LOG 0x01
+#define YH5151E_PAGE_5V_REAL 0x10
+#define YH5151E_PAGE_3V3_LOG 0x02
+#define YH5151E_PAGE_3V3_REAL 0x11
+
+enum chips {
+ ym2151e,
+ yh5151e
+};
+
+struct fsp3y_data {
+ struct pmbus_driver_info info;
+ int chip;
+ int page;
+};
+
+#define to_fsp3y_data(x) container_of(x, struct fsp3y_data, info)
+
+static int page_log_to_page_real(int page_log, enum chips chip)
+{
+ switch (chip) {
+ case ym2151e:
+ switch (page_log) {
+ case YM2151_PAGE_12V_LOG:
+ return YM2151_PAGE_12V_REAL;
+ case YM2151_PAGE_5VSB_LOG:
+ return YM2151_PAGE_5VSB_REAL;
+ }
+ return -EINVAL;
+ case yh5151e:
+ switch (page_log) {
+ case YH5151E_PAGE_12V_LOG:
+ return YH5151E_PAGE_12V_REAL;
+ case YH5151E_PAGE_5V_LOG:
+ return YH5151E_PAGE_5V_LOG;
+ case YH5151E_PAGE_3V3_LOG:
+ return YH5151E_PAGE_3V3_REAL;
+ }
+ return -EINVAL;
+ }
+
+ return -EINVAL;
+}
+
+static int set_page(struct i2c_client *client, int page_log)
+{
+ const struct pmbus_driver_info *info = pmbus_get_driver_info(client);
+ struct fsp3y_data *data = to_fsp3y_data(info);
+ int rv;
+ int page_real;
+
+ if (page_log < 0)
+ return 0;
+
+ page_real = page_log_to_page_real(page_log, data->chip);
+ if (page_real < 0)
+ return page_real;
+
+ if (data->page != page_real) {
+ rv = i2c_smbus_write_byte_data(client, PMBUS_PAGE, page_real);
+ if (rv < 0)
+ return rv;
+
+ data->page = page_real;
+
+ /*
+ * Testing showed that the device has a timing issue. After
+ * setting a page, it takes a while, before the device actually
+ * gives the correct values from the correct page. 20 ms was
+ * tested to be enough to not give wrong values (15 ms wasn't
+ * enough).
+ */
+ usleep_range(20000, 30000);
+ }
+
+ return 0;
+}
+
+static int fsp3y_read_byte_data(struct i2c_client *client, int page, int reg)
+{
+ int rv;
+
+ rv = set_page(client, page);
+ if (rv < 0)
+ return rv;
+
+ return i2c_smbus_read_byte_data(client, reg);
+}
+
+static int fsp3y_read_word_data(struct i2c_client *client, int page, int phase, int reg)
+{
+ int rv;
+
+ /*
+ * This masks commands which weren't tested to work correctly. Some of
+ * the masked commands return 0xFFFF. These would probably get tagged as
+ * invalid by pmbus_core. Other ones do return values which might be
+ * useful (that is, they are not 0xFFFF), but their encoding is unknown,
+ * and so they are unsupported.
+ */
+ switch (reg) {
+ case PMBUS_READ_FAN_SPEED_1:
+ case PMBUS_READ_IIN:
+ case PMBUS_READ_IOUT:
+ case PMBUS_READ_PIN:
+ case PMBUS_READ_POUT:
+ case PMBUS_READ_TEMPERATURE_1:
+ case PMBUS_READ_TEMPERATURE_2:
+ case PMBUS_READ_TEMPERATURE_3:
+ case PMBUS_READ_VIN:
+ case PMBUS_READ_VOUT:
+ case PMBUS_STATUS_WORD:
+ break;
+ default:
+ return -ENXIO;
+ }
+
+ rv = set_page(client, page);
+ if (rv < 0)
+ return rv;
+
+ return i2c_smbus_read_word_data(client, reg);
+}
+
+static struct pmbus_driver_info fsp3y_info[] = {
+ [ym2151e] = {
+ .pages = 2,
+ .func[YM2151_PAGE_12V_LOG] =
+ PMBUS_HAVE_VOUT | PMBUS_HAVE_IOUT |
+ PMBUS_HAVE_PIN | PMBUS_HAVE_POUT |
+ PMBUS_HAVE_TEMP | PMBUS_HAVE_TEMP2 |
+ PMBUS_HAVE_VIN | PMBUS_HAVE_IIN |
+ PMBUS_HAVE_FAN12,
+ .func[YM2151_PAGE_5VSB_LOG] =
+ PMBUS_HAVE_VOUT | PMBUS_HAVE_IOUT,
+ PMBUS_HAVE_IIN,
+ .read_word_data = fsp3y_read_word_data,
+ .read_byte_data = fsp3y_read_byte_data,
+ },
+ [yh5151e] = {
+ .pages = 3,
+ .func[YH5151E_PAGE_12V_LOG] =
+ PMBUS_HAVE_VOUT | PMBUS_HAVE_IOUT |
+ PMBUS_HAVE_POUT |
+ PMBUS_HAVE_TEMP | PMBUS_HAVE_TEMP2 | PMBUS_HAVE_TEMP3,
+ .func[YH5151E_PAGE_5V_LOG] =
+ PMBUS_HAVE_VOUT | PMBUS_HAVE_IOUT |
+ PMBUS_HAVE_POUT,
+ .func[YH5151E_PAGE_3V3_LOG] =
+ PMBUS_HAVE_VOUT | PMBUS_HAVE_IOUT |
+ PMBUS_HAVE_POUT,
+ .read_word_data = fsp3y_read_word_data,
+ .read_byte_data = fsp3y_read_byte_data,
+ }
+};
+
+static int fsp3y_detect(struct i2c_client *client)
+{
+ int rv;
+ u8 buf[I2C_SMBUS_BLOCK_MAX + 1];
+
+ rv = i2c_smbus_read_block_data(client, PMBUS_MFR_MODEL, buf);
+ if (rv < 0)
+ return rv;
+
+ buf[rv] = '\0';
+
+ if (rv == 8) {
+ if (!strcmp(buf, "YM-2151E"))
+ return ym2151e;
+ else if (!strcmp(buf, "YH-5151E"))
+ return yh5151e;
+ }
+
+ dev_err(&client->dev, "Unsupported model %.*s\n", rv, buf);
+ return -ENODEV;
+}
+
+static const struct i2c_device_id fsp3y_id[] = {
+ {"ym2151e", ym2151e},
+ {"yh5151e", yh5151e},
+ { }
+};
+
+static int fsp3y_probe(struct i2c_client *client)
+{
+ struct fsp3y_data *data;
+ const struct i2c_device_id *id;
+ int rv;
+
+ data = devm_kzalloc(&client->dev, sizeof(struct fsp3y_data), GFP_KERNEL);
+ if (!data)
+ return -ENOMEM;
+
+ data->chip = fsp3y_detect(client);
+ if (data->chip < 0)
+ return data->chip;
+
+ id = i2c_match_id(fsp3y_id, client);
+ if (data->chip != id->driver_data)
+ dev_warn(&client->dev, "Device mismatch: Configured %s (%d), detected %d\n",
+ id->name, (int)id->driver_data, data->chip);
+
+ rv = i2c_smbus_read_byte_data(client, PMBUS_PAGE);
+ if (rv < 0)
+ return rv;
+ data->page = rv;
+
+ data->info = fsp3y_info[data->chip];
+
+ return pmbus_do_probe(client, &data->info);
+}
+
+MODULE_DEVICE_TABLE(i2c, fsp3y_id);
+
+static struct i2c_driver fsp3y_driver = {
+ .driver = {
+ .name = "fsp3y",
+ },
+ .probe_new = fsp3y_probe,
+ .id_table = fsp3y_id
+};
+
+module_i2c_driver(fsp3y_driver);
+
+MODULE_AUTHOR("Václav Kubernát");
+MODULE_DESCRIPTION("PMBus driver for FSP/3Y-Power power supplies");
+MODULE_LICENSE("GPL");