SB-TSI hwmon driver v3

SB Temperature Sensor Interface (SB-TSI) is an SMBus compatible interface that reports AMD SoC's Ttcl (normalized temperature), and resembles a typical 8-pin remote temperature sensor's I2C interface to BMC.

This commit adds basic support using this interface to read CPU temperature, and read/write high/low CPU temp thresholds.

To instantiate this driver on an AMD CPU with SB-TSI
support, the i2c bus number would be the bus connected from the board management controller (BMC) to the CPU. The i2c address is specified in Section 6.3.1 of the spec [1]: The SB-TSI address is normally 98h for socket 0 and 90h for socket 1, but it could vary based on hardware address select pins.

[1]: https://www.amd.com/system/files/TechDocs/56255_OSRR.pdf

Test status: tested reading temp1_input, and reading/writing temp1_max/min.

Signed-off-by Kun Yi <[email protected]>

---
 drivers/hwmon/Kconfig      |  10 ++
 drivers/hwmon/Makefile     |   1 +
 drivers/hwmon/sbtsi_temp.c | 259 +++++++++++++++++++++++++++++++++++++
 3 files changed, 270 insertions(+)
 create mode 100644 drivers/hwmon/sbtsi_temp.c

drivers/hwmon/Kconfig +10 -0

index 05a30832c6ba..9585dcd01d1b 100644
@@ -1412,6 +1412,16 @@ config SENSORS_RASPBERRYPI_HWMON
 	  This driver can also be built as a module. If so, the module
 	  will be called raspberrypi-hwmon.
 
+config SENSORS_SBTSI
+	tristate "Emulated SB-TSI temperature sensor"
+	depends on I2C
+	help
+	  If you say yes here you get support for emulated temperature
+	  sensors on AMD SoCs with SB-TSI interface connected to a BMC device.
+
+	  This driver can also be built as a module. If so, the module will
+	  be called sbtsi_temp.
+
 config SENSORS_SHT15
 	tristate "Sensiron humidity and temperature sensors. SHT15 and compat."
 	depends on GPIOLIB || COMPILE_TEST

drivers/hwmon/Makefile +1 -0

index b0b9c8e57176..cd109f003ce4 100644
@@ -152,6 +152,7 @@ obj-$(CONFIG_SENSORS_POWR1220)  += powr1220.o
 obj-$(CONFIG_SENSORS_PWM_FAN)	+= pwm-fan.o
 obj-$(CONFIG_SENSORS_RASPBERRYPI_HWMON)	+= raspberrypi-hwmon.o
 obj-$(CONFIG_SENSORS_S3C)	+= s3c-hwmon.o
+obj-$(CONFIG_SENSORS_SBTSI)	+= sbtsi_temp.o
 obj-$(CONFIG_SENSORS_SCH56XX_COMMON)+= sch56xx-common.o
 obj-$(CONFIG_SENSORS_SCH5627)	+= sch5627.o
 obj-$(CONFIG_SENSORS_SCH5636)	+= sch5636.o

drivers/hwmon/sbtsi_temp.c new file +22 -0

new file mode 100644
index 000000000000..e3ad6a9f7ec1
@@ -0,0 +1,259 @@
+// SPDX-License-Identifier: GPL-2.0-or-later
+/*
+ * sbtsi_temp.c - hwmon driver for a SBI Temperature Sensor Interface (SB-TSI)
+ *                compliant AMD SoC temperature device.
+ *
+ * Copyright (c) 2020, Google Inc.
+ * Copyright (c) 2020, Kun Yi <[email protected]>
+ */
+
+#include <linux/err.h>
+#include <linux/i2c.h>
+#include <linux/init.h>
+#include <linux/hwmon.h>
+#include <linux/module.h>
+#include <linux/mutex.h>
+#include <linux/of_device.h>
+#include <linux/of.h>
+
+/*
+ * SB-TSI registers only support SMBus byte data access. "_INT" registers are
+ * the integer part of a temperature value or limit, and "_DEC" registers are
+ * corresponding decimal parts.

drivers/hwmon/sbtsi_temp.c new file +51 -0

+
+/* Each client has this additional data */
+struct sbtsi_data {
+	struct i2c_client *client;
+	struct mutex lock;
+};
+
+/*
+ * From SB-TSI spec: CPU temperature readings and limit registers encode the
+ * temperature in increments of 0.125 from 0 to 255.875. The "high byte"
+ * register encodes the base-2 of the integer portion, and the upper 3 bits of
+ * the "low byte" encode in base-2 the decimal portion.
+ *
+ * e.g. INT=0x19, DEC=0x20 represents 25.125 degrees Celsius
+ *
+ * Therefore temperature in millidegree Celsius =
+ *   (INT + DEC / 256) * 1000 = (INT * 8 + DEC / 32) * 125
+ */
+static inline int sbtsi_reg_to_mc(s32 integer, s32 decimal)
+{
+	return ((integer << 3) + (decimal >> 5)) * 125;
+}
+
+/*
+ * Inversely, given temperature in millidegree Celsius
+ *   INT = (TEMP / 125) / 8
+ *   DEC = ((TEMP / 125) % 8) * 32
+ * Caller have to make sure temp doesn't exceed 255875, the max valid value.
+ */
+static inline void sbtsi_mc_to_reg(s32 temp, u8 *integer, u8 *decimal)
+{
+	temp /= 125;
+	*integer = temp >> 3;
+	*decimal = (temp & 0x7) << 5;
+}
+
+static int sbtsi_read(struct device *dev, enum hwmon_sensor_types type,
+		      u32 attr, int channel, long *val)
+{
+	struct sbtsi_data *data = dev_get_drvdata(dev);
+	s32 temp_int, temp_dec;
+	int err, reg_int, reg_dec;
+	u8 read_order;
+
+	if (type != hwmon_temp)
+		return -EINVAL;
+
+	read_order = 0;
+	switch (attr) {
+	case hwmon_temp_input:
+		/*

drivers/hwmon/sbtsi_temp.c new file +12 -0

+		reg_int = SBTSI_REG_TEMP_INT;
+		reg_dec = SBTSI_REG_TEMP_DEC;
+		break;
+	case hwmon_temp_max:
+		reg_int = SBTSI_REG_TEMP_HIGH_INT;
+		reg_dec = SBTSI_REG_TEMP_HIGH_DEC;
+		break;
+	case hwmon_temp_min:
+		reg_int = SBTSI_REG_TEMP_LOW_INT;
+		reg_dec = SBTSI_REG_TEMP_LOW_DEC;
+		break;
+	default:

drivers/hwmon/sbtsi_temp.c new file +63 -0

+
+	if (temp_int < 0)
+		return temp_int;
+	if (temp_dec < 0)
+		return temp_dec;
+
+	*val = sbtsi_reg_to_mc(temp_int, temp_dec);
+
+	return 0;
+}
+
+static int sbtsi_write(struct device *dev, enum hwmon_sensor_types type,
+		       u32 attr, int channel, long val)
+{
+	struct sbtsi_data *data = dev_get_drvdata(dev);
+	int reg_int, reg_dec, err;
+	u8 temp_int, temp_dec;
+
+	if (type != hwmon_temp)
+		return -EINVAL;
+
+	switch (attr) {
+	case hwmon_temp_max:
+		reg_int = SBTSI_REG_TEMP_HIGH_INT;
+		reg_dec = SBTSI_REG_TEMP_HIGH_DEC;
+		break;
+	case hwmon_temp_min:
+		reg_int = SBTSI_REG_TEMP_LOW_INT;
+		reg_dec = SBTSI_REG_TEMP_LOW_DEC;
+		break;
+	default:
+		return -EINVAL;
+	}
+
+	val = clamp_val(val, SBTSI_TEMP_MIN, SBTSI_TEMP_MAX);
+	mutex_lock(&data->lock);
+	sbtsi_mc_to_reg(val, &temp_int, &temp_dec);
+	err = i2c_smbus_write_byte_data(data->client, reg_int, temp_int);
+	if (err)
+		goto exit;
+
+	err = i2c_smbus_write_byte_data(data->client, reg_dec, temp_dec);
+exit:
+	mutex_unlock(&data->lock);
+	return err;
+}
+
+static umode_t sbtsi_is_visible(const void *data,
+				enum hwmon_sensor_types type,
+				u32 attr, int channel)
+{
+	switch (type) {
+	case hwmon_temp:
+		switch (attr) {
+		case hwmon_temp_input:
+			return 0444;
+		case hwmon_temp_min:
+			return 0644;
+		case hwmon_temp_max:
+			return 0644;
+		}
+		break;
+	default:

drivers/hwmon/sbtsi_temp.c new file +64 -0

+	NULL
+};
+
+static const struct hwmon_ops sbtsi_hwmon_ops = {
+	.is_visible = sbtsi_is_visible,
+	.read = sbtsi_read,
+	.write = sbtsi_write,
+};
+
+static const struct hwmon_chip_info sbtsi_chip_info = {
+	.ops = &sbtsi_hwmon_ops,
+	.info = sbtsi_info,
+};
+
+static int sbtsi_probe(struct i2c_client *client,
+		       const struct i2c_device_id *id)
+{
+	struct device *dev = &client->dev;
+	struct device *hwmon_dev;
+	struct sbtsi_data *data;
+
+	data = devm_kzalloc(dev, sizeof(struct sbtsi_data), GFP_KERNEL);
+	if (!data)
+		return -ENOMEM;
+
+	data->client = client;
+	mutex_init(&data->lock);
+
+	hwmon_dev =
+		devm_hwmon_device_register_with_info(dev, client->name, data,
+						     &sbtsi_chip_info, NULL);
+
+	return PTR_ERR_OR_ZERO(hwmon_dev);
+}
+
+static const struct i2c_device_id sbtsi_id[] = {
+	{"sbtsi", 0},
+	{}
+};
+MODULE_DEVICE_TABLE(i2c, sbtsi_id);
+
+static const struct of_device_id __maybe_unused sbtsi_of_match[] = {
+	{
+		.compatible = "amd,sbtsi",
+	},
+	{ },
+};
+MODULE_DEVICE_TABLE(of, sbtsi_of_match);
+
+static struct i2c_driver sbtsi_driver = {
+	.class = I2C_CLASS_HWMON,
+	.driver = {
+		.name = "sbtsi",
+		.of_match_table = of_match_ptr(sbtsi_of_match),
+	},
+	.probe = sbtsi_probe,
+	.id_table = sbtsi_id,
+};
+
+module_i2c_driver(sbtsi_driver);
+
+MODULE_AUTHOR("Kun Yi <[email protected]>");
+MODULE_DESCRIPTION("Hwmon driver for AMD SB-TSI emulated sensor");
+MODULE_LICENSE("GPL");

Document device tree bindings for AMD SB-TSI emulated temperature sensor.

Signed-off-by Kun Yi <[email protected]>

---
 .../devicetree/bindings/hwmon/amd,sbtsi.txt   | 26 +++++++++++++++++++
 1 file changed, 26 insertions(+)
 create mode 100644 Documentation/devicetree/bindings/hwmon/amd,sbtsi.txt

Documentation/devicetree/bindings/hwmon/amd,sbtsi.txt new file +16 -0

new file mode 100644
index 000000000000..be7293c43c0e
@@ -0,0 +1,26 @@
+* Sideband interface Temperature Sensor Interface (SB-TSI) compliant
+AMD SoC temperature device.
+
+SB Temperature Sensor Interface (SB-TSI) is an SMBus compatible
+interface that reports AMD SoC's Ttcl (normalized temperature),
+and resembles a typical 8-pin remote temperature sensor's I2C interface
+to BMC. The emulated thermal sensor can report temperatures in increments of
+0.125 degrees, ranging from 0 to 255.875.
+
+Required properties:
+- compatible: manufacturer and chip name, should be
+	"amd,sbtsi",
+
+- reg: I2C bus address of the device as specified in Section 6.3.1 of the
+SoC register reference: The SB-TSI address is normally 98h for socket 0 and
+90h for socket 1, but it could vary based on hardware address select pins.