hwmon: Add support for SB-RMI power module

On AMD platforms the Out-of-band access is provided by
Advanced Platform Management Link (APML), APML is a
SMBus v2.0 compatible 2-wire processor client interface.
APML is also referred as the sideband interface (SBI).

APML is used to communicate with the
Side-Band Remote Management Interface (SB-RMI) which provides
Soft Mailbox messages to manage power consumption and
power limits of the CPU socket.

- This module add support to read power consumption,
power limit & max power limit and write power limit.
- To instantiate this driver on a Board Management Controller (BMC)
connected to an AMD CPU with SB-RMI support, the i2c bus number
would be the bus connected from the BMC to the CPU.

Reviewed-by: Guenter Roeck <[e-mail]>
Signed-off-by: Akshay Gupta <[e-mail]>
Signed-off-by: Naveen Krishna Chatradhi <[e-mail]>
Link: https://lore.kernel.org/r/[e-mail]
[groeck: Fix uninitialized variable problem when reporting max power]
Signed-off-by: Guenter Roeck <[e-mail]>

drivers/hwmon/Kconfig

···
 	  This driver can also be built as a module. If so, the module will
 	  be called sbtsi_temp.
 
+config SENSORS_SBRMI
+	tristate "Emulated SB-RMI sensor"
+	depends on I2C
+	help
+	  If you say yes here you get support for emulated RMI
+	  sensors on AMD SoCs with APML interface connected to a BMC device.
+
+	  This driver can also be built as a module. If so, the module will
+	  be called sbrmi.
+
 config SENSORS_SHT15
 	tristate "Sensiron humidity and temperature sensors. SHT15 and compat."
 	depends on GPIOLIB || COMPILE_TEST

drivers/hwmon/Makefile

···
 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_SBRMI)	+= sbrmi.o
 obj-$(CONFIG_SENSORS_SCH56XX_COMMON)+= sch56xx-common.o
 obj-$(CONFIG_SENSORS_SCH5627)	+= sch5627.o
 obj-$(CONFIG_SENSORS_SCH5636)	+= sch5636.o

drivers/hwmon/sbrmi.c

···
+// SPDX-License-Identifier: GPL-2.0-or-later
+/*
+ * sbrmi.c - hwmon driver for a SB-RMI mailbox
+ *           compliant AMD SoC device.
+ *
+ * Copyright (C) 2020-2021 Advanced Micro Devices, Inc.
+ */
+
+#include <linux/delay.h>
+#include <linux/err.h>
+#include <linux/hwmon.h>
+#include <linux/i2c.h>
+#include <linux/init.h>
+#include <linux/module.h>
+#include <linux/mutex.h>
+#include <linux/of.h>
+
+/* Do not allow setting negative power limit */
+#define SBRMI_PWR_MIN	0
+/* Mask for Status Register bit[1] */
+#define SW_ALERT_MASK	0x2
+
+/* Software Interrupt for triggering */
+#define START_CMD	0x80
+#define TRIGGER_MAILBOX	0x01
+
+/*
+ * SB-RMI supports soft mailbox service request to MP1 (power management
+ * firmware) through SBRMI inbound/outbound message registers.
+ * SB-RMI message IDs
+ */
+enum sbrmi_msg_id {
+	SBRMI_READ_PKG_PWR_CONSUMPTION = 0x1,
+	SBRMI_WRITE_PKG_PWR_LIMIT,
+	SBRMI_READ_PKG_PWR_LIMIT,
+	SBRMI_READ_PKG_MAX_PWR_LIMIT,
+};
+
+/* SB-RMI registers */
+enum sbrmi_reg {
+	SBRMI_CTRL		= 0x01,
+	SBRMI_STATUS,
+	SBRMI_OUTBNDMSG0	= 0x30,
+	SBRMI_OUTBNDMSG1,
+	SBRMI_OUTBNDMSG2,
+	SBRMI_OUTBNDMSG3,
+	SBRMI_OUTBNDMSG4,
+	SBRMI_OUTBNDMSG5,
+	SBRMI_OUTBNDMSG6,
+	SBRMI_OUTBNDMSG7,
+	SBRMI_INBNDMSG0,
+	SBRMI_INBNDMSG1,
+	SBRMI_INBNDMSG2,
+	SBRMI_INBNDMSG3,
+	SBRMI_INBNDMSG4,
+	SBRMI_INBNDMSG5,
+	SBRMI_INBNDMSG6,
+	SBRMI_INBNDMSG7,
+	SBRMI_SW_INTERRUPT,
+};
+
+/* Each client has this additional data */
+struct sbrmi_data {
+	struct i2c_client *client;
+	struct mutex lock;
+	u32 pwr_limit_max;
+};
+
+struct sbrmi_mailbox_msg {
+	u8 cmd;
+	bool read;
+	u32 data_in;
+	u32 data_out;
+};
+
+static int sbrmi_enable_alert(struct i2c_client *client)
+{
+	int ctrl;
+
+	/*
+	 * Enable the SB-RMI Software alert status
+	 * by writing 0 to bit 4 of Control register(0x1)
+	 */
+	ctrl = i2c_smbus_read_byte_data(client, SBRMI_CTRL);
+	if (ctrl < 0)
+		return ctrl;
+
+	if (ctrl & 0x10) {
+		ctrl &= ~0x10;
+		return i2c_smbus_write_byte_data(client,
+						 SBRMI_CTRL, ctrl);
+	}
+
+	return 0;
+}
+
+static int rmi_mailbox_xfer(struct sbrmi_data *data,
+			    struct sbrmi_mailbox_msg *msg)
+{
+	int i, ret, retry = 10;
+	int sw_status;
+	u8 byte;
+
+	mutex_lock(&data->lock);
+
+	/* Indicate firmware a command is to be serviced */
+	ret = i2c_smbus_write_byte_data(data->client,
+					SBRMI_INBNDMSG7, START_CMD);
+	if (ret < 0)
+		goto exit_unlock;
+
+	/* Write the command to SBRMI::InBndMsg_inst0 */
+	ret = i2c_smbus_write_byte_data(data->client,
+					SBRMI_INBNDMSG0, msg->cmd);
+	if (ret < 0)
+		goto exit_unlock;
+
+	/*
+	 * For both read and write the initiator (BMC) writes
+	 * Command Data In[31:0] to SBRMI::InBndMsg_inst[4:1]
+	 * SBRMI_x3C(MSB):SBRMI_x39(LSB)
+	 */
+	for (i = 0; i < 4; i++) {
+		byte = (msg->data_in >> i * 8) & 0xff;
+		ret = i2c_smbus_write_byte_data(data->client,
+						SBRMI_INBNDMSG1 + i, byte);
+		if (ret < 0)
+			goto exit_unlock;
+	}
+
+	/*
+	 * Write 0x01 to SBRMI::SoftwareInterrupt to notify firmware to
+	 * perform the requested read or write command
+	 */
+	ret = i2c_smbus_write_byte_data(data->client,
+					SBRMI_SW_INTERRUPT, TRIGGER_MAILBOX);
+	if (ret < 0)
+		goto exit_unlock;
+
+	/*
+	 * Firmware will write SBRMI::Status[SwAlertSts]=1 to generate
+	 * an ALERT (if enabled) to initiator (BMC) to indicate completion
+	 * of the requested command
+	 */
+	do {
+		sw_status = i2c_smbus_read_byte_data(data->client,
+						     SBRMI_STATUS);
+		if (sw_status < 0) {
+			ret = sw_status;
+			goto exit_unlock;
+		}
+		if (sw_status & SW_ALERT_MASK)
+			break;
+		usleep_range(50, 100);
+	} while (retry--);
+
+	if (retry < 0) {
+		dev_err(&data->client->dev,
+			"Firmware fail to indicate command completion\n");
+		ret = -EIO;
+		goto exit_unlock;
+	}
+
+	/*
+	 * For a read operation, the initiator (BMC) reads the firmware
+	 * response Command Data Out[31:0] from SBRMI::OutBndMsg_inst[4:1]
+	 * {SBRMI_x34(MSB):SBRMI_x31(LSB)}.
+	 */
+	if (msg->read) {
+		for (i = 0; i < 4; i++) {
+			ret = i2c_smbus_read_byte_data(data->client,
+						       SBRMI_OUTBNDMSG1 + i);
+			if (ret < 0)
+				goto exit_unlock;
+			msg->data_out |= ret << i * 8;
+		}
+	}
+
+	/*
+	 * BMC must write 1'b1 to SBRMI::Status[SwAlertSts] to clear the
+	 * ALERT to initiator
+	 */
+	ret = i2c_smbus_write_byte_data(data->client, SBRMI_STATUS,
+					sw_status | SW_ALERT_MASK);
+
+exit_unlock:
+	mutex_unlock(&data->lock);
+	return ret;
+}
+
+static int sbrmi_read(struct device *dev, enum hwmon_sensor_types type,
+		      u32 attr, int channel, long *val)
+{
+	struct sbrmi_data *data = dev_get_drvdata(dev);
+	struct sbrmi_mailbox_msg msg = { 0 };
+	int ret;
+
+	if (type != hwmon_power)
+		return -EINVAL;
+
+	msg.read = true;
+	switch (attr) {
+	case hwmon_power_input:
+		msg.cmd = SBRMI_READ_PKG_PWR_CONSUMPTION;
+		ret = rmi_mailbox_xfer(data, &msg);
+		break;
+	case hwmon_power_cap:
+		msg.cmd = SBRMI_READ_PKG_PWR_LIMIT;
+		ret = rmi_mailbox_xfer(data, &msg);
+		break;
+	case hwmon_power_cap_max:
+		msg.data_out = data->pwr_limit_max;
+		ret = 0;
+		break;
+	default:
+		return -EINVAL;
+	}
+	if (ret < 0)
+		return ret;
+	/* hwmon power attributes are in microWatt */
+	*val = (long)msg.data_out * 1000;
+	return ret;
+}
+
+static int sbrmi_write(struct device *dev, enum hwmon_sensor_types type,
+		       u32 attr, int channel, long val)
+{
+	struct sbrmi_data *data = dev_get_drvdata(dev);
+	struct sbrmi_mailbox_msg msg = { 0 };
+
+	if (type != hwmon_power && attr != hwmon_power_cap)
+		return -EINVAL;
+	/*
+	 * hwmon power attributes are in microWatt
+	 * mailbox read/write is in mWatt
+	 */
+	val /= 1000;
+
+	val = clamp_val(val, SBRMI_PWR_MIN, data->pwr_limit_max);
+
+	msg.cmd = SBRMI_WRITE_PKG_PWR_LIMIT;
+	msg.data_in = val;
+	msg.read = false;
+
+	return rmi_mailbox_xfer(data, &msg);
+}
+
+static umode_t sbrmi_is_visible(const void *data,
+				enum hwmon_sensor_types type,
+				u32 attr, int channel)
+{
+	switch (type) {
+	case hwmon_power:
+		switch (attr) {
+		case hwmon_power_input:
+		case hwmon_power_cap_max:
+			return 0444;
+		case hwmon_power_cap:
+			return 0644;
+		}
+		break;
+	default:
+		break;
+	}
+	return 0;
+}
+
+static const struct hwmon_channel_info *sbrmi_info[] = {
+	HWMON_CHANNEL_INFO(power,
+			   HWMON_P_INPUT | HWMON_P_CAP | HWMON_P_CAP_MAX),
+	NULL
+};
+
+static const struct hwmon_ops sbrmi_hwmon_ops = {
+	.is_visible = sbrmi_is_visible,
+	.read = sbrmi_read,
+	.write = sbrmi_write,
+};
+
+static const struct hwmon_chip_info sbrmi_chip_info = {
+	.ops = &sbrmi_hwmon_ops,
+	.info = sbrmi_info,
+};
+
+static int sbrmi_get_max_pwr_limit(struct sbrmi_data *data)
+{
+	struct sbrmi_mailbox_msg msg = { 0 };
+	int ret;
+
+	msg.cmd = SBRMI_READ_PKG_MAX_PWR_LIMIT;
+	msg.read = true;
+	ret = rmi_mailbox_xfer(data, &msg);
+	if (ret < 0)
+		return ret;
+	data->pwr_limit_max = msg.data_out;
+
+	return ret;
+}
+
+static int sbrmi_probe(struct i2c_client *client,
+		       const struct i2c_device_id *id)
+{
+	struct device *dev = &client->dev;
+	struct device *hwmon_dev;
+	struct sbrmi_data *data;
+	int ret;
+
+	data = devm_kzalloc(dev, sizeof(struct sbrmi_data), GFP_KERNEL);
+	if (!data)
+		return -ENOMEM;
+
+	data->client = client;
+	mutex_init(&data->lock);
+
+	/* Enable alert for SB-RMI sequence */
+	ret = sbrmi_enable_alert(client);
+	if (ret < 0)
+		return ret;
+
+	/* Cache maximum power limit */
+	ret = sbrmi_get_max_pwr_limit(data);
+	if (ret < 0)
+		return ret;
+
+	hwmon_dev = devm_hwmon_device_register_with_info(dev, client->name, data,
+							 &sbrmi_chip_info, NULL);
+
+	return PTR_ERR_OR_ZERO(hwmon_dev);
+}
+
+static const struct i2c_device_id sbrmi_id[] = {
+	{"sbrmi", 0},
+	{}
+};
+MODULE_DEVICE_TABLE(i2c, sbrmi_id);
+
+static const struct of_device_id __maybe_unused sbrmi_of_match[] = {
+	{
+		.compatible = "amd,sbrmi",
+	},
+	{ },
+};
+MODULE_DEVICE_TABLE(of, sbrmi_of_match);
+
+static struct i2c_driver sbrmi_driver = {
+	.class = I2C_CLASS_HWMON,
+	.driver = {
+		.name = "sbrmi",
+		.of_match_table = of_match_ptr(sbrmi_of_match),
+	},
+	.probe = sbrmi_probe,
+	.id_table = sbrmi_id,
+};
+
+module_i2c_driver(sbrmi_driver);
+
+MODULE_AUTHOR("Akshay Gupta <[e-mail]>");
+MODULE_DESCRIPTION("Hwmon driver for AMD SB-RMI emulated sensor");
+MODULE_LICENSE("GPL");