hwmon: Add LattePanda Sigma EC driver

Add hardware monitoring support for the LattePanda Sigma SBC
(DFRobot, ITE IT8613E EC). The driver reads fan speed and
temperatures via direct port I/O, as the BIOS disables the
ACPI EC interface.

Signed-off-by: Mariano Abad <weimaraner@gmail.com>
Signed-off-by: Guenter Roeck <linux@roeck-us.net>

3 files changed, 377 insertions, 0 deletions

diff --git a/drivers/hwmon/Kconfig b/drivers/hwmon/Kconfig
index f034d204be4f..e0cd83b4b715 100644
--- a/drivers/hwmon/Kconfig
+++ b/drivers/hwmon/Kconfig
@@ -964,6 +964,23 @@ config SENSORS_LAN966X
 	  This driver can also be built as a module. If so, the module
 	  will be called lan966x-hwmon.
 
+config SENSORS_LATTEPANDA_SIGMA_EC
+	tristate "LattePanda Sigma EC hardware monitoring"
+	depends on X86
+	depends on DMI
+	depends on HAS_IOPORT
+	help
+	  If you say yes here you get support for the hardware monitoring
+	  features of the Embedded Controller on LattePanda Sigma
+	  single-board computers, including CPU fan speed (RPM) and
+	  board and CPU temperatures.
+
+	  The driver reads the EC directly via ACPI EC I/O ports and
+	  uses DMI matching to ensure it only loads on supported hardware.
+
+	  This driver can also be built as a module. If so, the module
+	  will be called lattepanda-sigma-ec.
+
 config SENSORS_LENOVO_EC
         tristate "Sensor reader for Lenovo ThinkStations"
         depends on X86
diff --git a/drivers/hwmon/Makefile b/drivers/hwmon/Makefile
index c1020dbbc1ac..556e86d277b1 100644
--- a/drivers/hwmon/Makefile
+++ b/drivers/hwmon/Makefile
@@ -113,6 +113,7 @@ obj-$(CONFIG_SENSORS_K10TEMP)	+= k10temp.o
 obj-$(CONFIG_SENSORS_KBATT)	+= kbatt.o
 obj-$(CONFIG_SENSORS_KFAN)	+= kfan.o
 obj-$(CONFIG_SENSORS_LAN966X)	+= lan966x-hwmon.o
+obj-$(CONFIG_SENSORS_LATTEPANDA_SIGMA_EC) += lattepanda-sigma-ec.o
 obj-$(CONFIG_SENSORS_LENOVO_EC)	+= lenovo-ec-sensors.o
 obj-$(CONFIG_SENSORS_LINEAGE)	+= lineage-pem.o
 obj-$(CONFIG_SENSORS_LOCHNAGAR)	+= lochnagar-hwmon.o
diff --git a/drivers/hwmon/lattepanda-sigma-ec.c b/drivers/hwmon/lattepanda-sigma-ec.c
new file mode 100644
index 000000000000..f06097422201
--- /dev/null
+++ b/drivers/hwmon/lattepanda-sigma-ec.c
@@ -0,0 +1,359 @@
+// SPDX-License-Identifier: GPL-2.0-or-later
+/*
+ * Hardware monitoring driver for LattePanda Sigma EC.
+ *
+ * The LattePanda Sigma is an x86 SBC made by DFRobot with an ITE IT8613E
+ * Embedded Controller that manages a CPU fan and thermal sensors.
+ *
+ * The BIOS declares the ACPI Embedded Controller (PNP0C09) with _STA
+ * returning 0 and provides only stub ECRD/ECWT methods that return Zero
+ * for all registers. Since the kernel's ACPI EC subsystem never initializes,
+ * ec_read() is not available and direct port I/O to the standard ACPI EC
+ * ports (0x62/0x66) is used instead.
+ *
+ * Because ACPI never initializes the EC, there is no concurrent firmware
+ * access to these ports, and no ACPI Global Lock or namespace mutex is
+ * required. The hwmon with_info API serializes all sysfs callbacks,
+ * so no additional driver-level locking is needed.
+ *
+ * The EC register map was discovered by dumping all 256 registers,
+ * identifying those that change in real-time, and validating by physically
+ * stopping the fan and observing the RPM register drop to zero. The map
+ * has been verified on BIOS version 5.27; other versions may differ.
+ *
+ * Copyright (c) 2026 Mariano Abad <weimaraner@gmail.com>
+ */
+
+#include <linux/delay.h>
+#include <linux/dmi.h>
+#include <linux/hwmon.h>
+#include <linux/io.h>
+#include <linux/ioport.h>
+#include <linux/module.h>
+#include <linux/platform_device.h>
+
+#define DRIVER_NAME	"lattepanda_sigma_ec"
+
+/* EC I/O ports (standard ACPI EC interface) */
+#define EC_DATA_PORT	0x62
+#define EC_CMD_PORT	0x66	/* also status port */
+
+/* EC commands */
+#define EC_CMD_READ	0x80
+
+/* EC status register bits */
+#define EC_STATUS_OBF	0x01	/* Output Buffer Full */
+#define EC_STATUS_IBF	0x02	/* Input Buffer Full */
+
+/* EC register offsets for LattePanda Sigma (BIOS 5.27) */
+#define EC_REG_FAN_RPM_HI	0x2E
+#define EC_REG_FAN_RPM_LO	0x2F
+#define EC_REG_TEMP_BOARD	0x60
+#define EC_REG_TEMP_CPU		0x70
+#define EC_REG_FAN_DUTY		0x93
+
+/*
+ * EC polling uses udelay() because the EC typically responds within a
+ * few microseconds. The kernel's own ACPI EC driver (drivers/acpi/ec.c)
+ * likewise uses udelay() for busy-polling with a per-poll delay of 550us.
+ *
+ * usleep_range() was tested but caused EC protocol failures: the EC
+ * clears its status flags within microseconds, and sleeping for 50-100us
+ * between polls allowed the flags to transition past the expected state.
+ *
+ * The worst-case total busy-wait of 25ms covers EC recovery after errors.
+ * In practice the EC responds within 10us so the loop exits immediately.
+ */
+#define EC_TIMEOUT_US		25000
+#define EC_POLL_US		1
+
+static bool force;
+module_param(force, bool, 0444);
+MODULE_PARM_DESC(force,
+		 "Force loading on untested BIOS versions (default: false)");
+
+static struct platform_device *lps_ec_pdev;
+
+static int ec_wait_ibf_clear(void)
+{
+	int i;
+
+	for (i = 0; i < EC_TIMEOUT_US; i++) {
+		if (!(inb(EC_CMD_PORT) & EC_STATUS_IBF))
+			return 0;
+		udelay(EC_POLL_US);
+	}
+	return -ETIMEDOUT;
+}
+
+static int ec_wait_obf_set(void)
+{
+	int i;
+
+	for (i = 0; i < EC_TIMEOUT_US; i++) {
+		if (inb(EC_CMD_PORT) & EC_STATUS_OBF)
+			return 0;
+		udelay(EC_POLL_US);
+	}
+	return -ETIMEDOUT;
+}
+
+static int ec_read_reg(u8 reg, u8 *val)
+{
+	int ret;
+
+	ret = ec_wait_ibf_clear();
+	if (ret)
+		return ret;
+
+	outb(EC_CMD_READ, EC_CMD_PORT);
+
+	ret = ec_wait_ibf_clear();
+	if (ret)
+		return ret;
+
+	outb(reg, EC_DATA_PORT);
+
+	ret = ec_wait_obf_set();
+	if (ret)
+		return ret;
+
+	*val = inb(EC_DATA_PORT);
+	return 0;
+}
+
+/*
+ * Read a 16-bit big-endian value from two consecutive EC registers.
+ *
+ * The EC may update the register pair between reading the high and low
+ * bytes, which could produce a corrupted value if the high byte rolls
+ * over (e.g., 0x0100 -> 0x00FF read as 0x01FF). Guard against this by
+ * re-reading the high byte after reading the low byte. If the high byte
+ * changed, re-read the low byte to get a consistent pair.
+ * See also lm90_read16() which uses the same approach.
+ */
+static int ec_read_reg16(u8 reg_hi, u8 reg_lo, u16 *val)
+{
+	int ret;
+	u8 oldh, newh, lo;
+
+	ret = ec_read_reg(reg_hi, &oldh);
+	if (ret)
+		return ret;
+
+	ret = ec_read_reg(reg_lo, &lo);
+	if (ret)
+		return ret;
+
+	ret = ec_read_reg(reg_hi, &newh);
+	if (ret)
+		return ret;
+
+	if (oldh != newh) {
+		ret = ec_read_reg(reg_lo, &lo);
+		if (ret)
+			return ret;
+	}
+
+	*val = ((u16)newh << 8) | lo;
+	return 0;
+}
+
+static int
+lps_ec_read_string(struct device *dev,
+		   enum hwmon_sensor_types type,
+		   u32 attr, int channel,
+		   const char **str)
+{
+	switch (type) {
+	case hwmon_fan:
+		*str = "CPU Fan";
+		return 0;
+	case hwmon_temp:
+		*str = channel == 0 ? "Board Temp" : "CPU Temp";
+		return 0;
+	default:
+		return -EOPNOTSUPP;
+	}
+}
+
+static umode_t
+lps_ec_is_visible(const void *drvdata,
+		  enum hwmon_sensor_types type,
+		  u32 attr, int channel)
+{
+	switch (type) {
+	case hwmon_fan:
+		if (attr == hwmon_fan_input || attr == hwmon_fan_label)
+			return 0444;
+		break;
+	case hwmon_temp:
+		if (attr == hwmon_temp_input || attr == hwmon_temp_label)
+			return 0444;
+		break;
+	default:
+		break;
+	}
+	return 0;
+}
+
+static int
+lps_ec_read(struct device *dev,
+	    enum hwmon_sensor_types type,
+	    u32 attr, int channel, long *val)
+{
+	u16 rpm;
+	u8 v;
+	int ret;
+
+	switch (type) {
+	case hwmon_fan:
+		if (attr != hwmon_fan_input)
+			return -EOPNOTSUPP;
+		ret = ec_read_reg16(EC_REG_FAN_RPM_HI,
+				    EC_REG_FAN_RPM_LO, &rpm);
+		if (ret)
+			return ret;
+		*val = rpm;
+		return 0;
+
+	case hwmon_temp:
+		if (attr != hwmon_temp_input)
+			return -EOPNOTSUPP;
+		ret = ec_read_reg(channel == 0 ? EC_REG_TEMP_BOARD
+					       : EC_REG_TEMP_CPU,
+				  &v);
+		if (ret)
+			return ret;
+		/* EC reports unsigned 8-bit temperature in degrees Celsius */
+		*val = (unsigned long)v * 1000;
+		return 0;
+
+	default:
+		return -EOPNOTSUPP;
+	}
+}
+
+static const struct hwmon_channel_info * const lps_ec_info[] = {
+	HWMON_CHANNEL_INFO(fan, HWMON_F_INPUT | HWMON_F_LABEL),
+	HWMON_CHANNEL_INFO(temp,
+			   HWMON_T_INPUT | HWMON_T_LABEL,
+			   HWMON_T_INPUT | HWMON_T_LABEL),
+	NULL
+};
+
+static const struct hwmon_ops lps_ec_ops = {
+	.is_visible = lps_ec_is_visible,
+	.read = lps_ec_read,
+	.read_string = lps_ec_read_string,
+};
+
+static const struct hwmon_chip_info lps_ec_chip_info = {
+	.ops = &lps_ec_ops,
+	.info = lps_ec_info,
+};
+
+static int lps_ec_probe(struct platform_device *pdev)
+{
+	struct device *dev = &pdev->dev;
+	struct device *hwmon;
+	u8 test;
+	int ret;
+
+	if (!devm_request_region(dev, EC_DATA_PORT, 1, DRIVER_NAME))
+		return dev_err_probe(dev, -EBUSY,
+				     "Failed to request EC data port 0x%x\n",
+				     EC_DATA_PORT);
+
+	if (!devm_request_region(dev, EC_CMD_PORT, 1, DRIVER_NAME))
+		return dev_err_probe(dev, -EBUSY,
+				     "Failed to request EC cmd port 0x%x\n",
+				     EC_CMD_PORT);
+
+	/* Sanity check: verify EC is responsive */
+	ret = ec_read_reg(EC_REG_FAN_DUTY, &test);
+	if (ret)
+		return dev_err_probe(dev, ret,
+				     "EC not responding on ports 0x%x/0x%x\n",
+				     EC_DATA_PORT, EC_CMD_PORT);
+
+	hwmon = devm_hwmon_device_register_with_info(dev, DRIVER_NAME, NULL,
+						     &lps_ec_chip_info, NULL);
+	if (IS_ERR(hwmon))
+		return dev_err_probe(dev, PTR_ERR(hwmon),
+				     "Failed to register hwmon device\n");
+
+	dev_info(dev, "EC hwmon registered (fan duty: %u%%)\n", test);
+	return 0;
+}
+
+/* DMI table with strict BIOS version match (override with force=1) */
+static const struct dmi_system_id lps_ec_dmi_table[] = {
+	{
+		.ident = "LattePanda Sigma",
+		.matches = {
+			DMI_MATCH(DMI_SYS_VENDOR, "LattePanda"),
+			DMI_MATCH(DMI_PRODUCT_NAME, "LattePanda Sigma"),
+			DMI_MATCH(DMI_BIOS_VERSION, "5.27"),
+		},
+	},
+	{ }	/* terminator */
+};
+MODULE_DEVICE_TABLE(dmi, lps_ec_dmi_table);
+
+/* Loose table (vendor + product only) for use with force=1 */
+static const struct dmi_system_id lps_ec_dmi_table_force[] = {
+	{
+		.ident = "LattePanda Sigma",
+		.matches = {
+			DMI_MATCH(DMI_SYS_VENDOR, "LattePanda"),
+			DMI_MATCH(DMI_PRODUCT_NAME, "LattePanda Sigma"),
+		},
+	},
+	{ }	/* terminator */
+};
+
+static struct platform_driver lps_ec_driver = {
+	.probe	= lps_ec_probe,
+	.driver	= {
+		.name = DRIVER_NAME,
+	},
+};
+
+static int __init lps_ec_init(void)
+{
+	int ret;
+
+	if (!dmi_check_system(lps_ec_dmi_table)) {
+		if (!force || !dmi_check_system(lps_ec_dmi_table_force))
+			return -ENODEV;
+		pr_warn("%s: BIOS version not verified, loading due to force=1\n",
+			DRIVER_NAME);
+	}
+
+	ret = platform_driver_register(&lps_ec_driver);
+	if (ret)
+		return ret;
+
+	lps_ec_pdev = platform_device_register_simple(DRIVER_NAME, -1,
+						      NULL, 0);
+	if (IS_ERR(lps_ec_pdev)) {
+		platform_driver_unregister(&lps_ec_driver);
+		return PTR_ERR(lps_ec_pdev);
+	}
+
+	return 0;
+}
+
+static void __exit lps_ec_exit(void)
+{
+	platform_device_unregister(lps_ec_pdev);
+	platform_driver_unregister(&lps_ec_driver);
+}
+
+module_init(lps_ec_init);
+module_exit(lps_ec_exit);
+
+MODULE_AUTHOR("Mariano Abad <weimaraner@gmail.com>");
+MODULE_DESCRIPTION("Hardware monitoring driver for LattePanda Sigma EC");
+MODULE_LICENSE("GPL");