--- /dev/null
+// 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");
projects / thirdparty / kernel / linux.git / commitdiff
