ACPI: fan: Add hwmon notification support

The platform firmware can notify the ACPI fan device that the fan
speed has changed. Relay this notification to the hwmon device if
present so that userspace applications can react to it.

Signed-off-by: Armin Wolf <[e-mail]>
Link: https://patch.msgid.link/[e-mail]
Signed-off-by: Rafael J. Wysocki <[e-mail]>

drivers/acpi/fan.h

···
 	struct acpi_fan_fif fif;
 	struct acpi_fan_fps *fps;
 	int fps_count;
+#if IS_REACHABLE(CONFIG_HWMON)
+	struct device *hdev;
+#endif
 	struct thermal_cooling_device *cdev;
 	struct device_attribute fst_speed;
 	struct device_attribute fine_grain_control;
···
 
 #if IS_REACHABLE(CONFIG_HWMON)
 int devm_acpi_fan_create_hwmon(struct device *dev);
+void acpi_fan_notify_hwmon(struct device *dev);
 #else
 static inline int devm_acpi_fan_create_hwmon(struct device *dev) { return 0; };
+static inline void acpi_fan_notify_hwmon(struct device *dev) { };
 #endif
 
 #endif

drivers/acpi/fan_core.c

···
 		if (ret < 0)
 			dev_err(dev, "Error retrieving current fan status: %d\n", ret);
 
+		acpi_fan_notify_hwmon(dev);
 		acpi_bus_generate_netlink_event("fan", dev_name(dev), event, 0);
 		break;
 	default:

drivers/acpi/fan_hwmon.c

···
 	.info = acpi_fan_hwmon_info,
 };
 
+void acpi_fan_notify_hwmon(struct device *dev)
+{
+	struct acpi_fan *fan = dev_get_drvdata(dev);
+
+	hwmon_notify_event(fan->hdev, hwmon_fan, hwmon_fan_input, 0);
+}
+
 int devm_acpi_fan_create_hwmon(struct device *dev)
 {
 	struct acpi_fan *fan = dev_get_drvdata(dev);
-	struct device *hdev;
 
-	hdev = devm_hwmon_device_register_with_info(dev, "acpi_fan", fan, &acpi_fan_hwmon_chip_info,
-						    NULL);
-	return PTR_ERR_OR_ZERO(hdev);
+	fan->hdev = devm_hwmon_device_register_with_info(dev, "acpi_fan", fan,
+							 &acpi_fan_hwmon_chip_info, NULL);
+
+	return PTR_ERR_OR_ZERO(fan->hdev);
 }