[PATCH v2] ACPI: fan: Add hwmon support

[Armin Wolf <W_Armin@gmx.de>]

Currently, the driver does only support a custom sysfs
to allow userspace to read the fan speed.
Add support for the standard hwmon interface so users
can read the fan speed with standard tools like "sensors".

Compile-tested only.

Signed-off-by: Armin Wolf <W_Armin@gmx.de>
---
Changes since v1:
- fix undefined reference error
- fix fan speed validation
- coding style fixes
- clarify that the changes are compile-tested only
- add hwmon maintainers to cc list

The changes will be tested by Mikael Lund Jepsen from Danelec and
should be merged only after those tests.
---
 drivers/acpi/Makefile    |  1 +
 drivers/acpi/fan.h       |  9 +++++
 drivers/acpi/fan_core.c  |  4 ++
 drivers/acpi/fan_hwmon.c | 83 ++++++++++++++++++++++++++++++++++++++++
 4 files changed, 97 insertions(+)
 create mode 100644 drivers/acpi/fan_hwmon.c

diff --git a/drivers/acpi/Makefile b/drivers/acpi/Makefile
index d69d5444acdb..c272ab2c93b9 100644
--- a/drivers/acpi/Makefile
+++ b/drivers/acpi/Makefile
@@ -83,6 +83,7 @@ obj-$(CONFIG_ACPI_TINY_POWER_BUTTON)	+= tiny-power-button.o
 obj-$(CONFIG_ACPI_FAN)		+= fan.o
 fan-objs			:= fan_core.o
 fan-objs			+= fan_attr.o
+fan-$(CONFIG_HWMON)		+= fan_hwmon.o

 obj-$(CONFIG_ACPI_VIDEO)	+= video.o
 obj-$(CONFIG_ACPI_TAD)		+= acpi_tad.o
diff --git a/drivers/acpi/fan.h b/drivers/acpi/fan.h
index e7b4b4e4a55e..97863bdb6303 100644
--- a/drivers/acpi/fan.h
+++ b/drivers/acpi/fan.h
@@ -10,6 +10,8 @@
 #ifndef _ACPI_FAN_H_
 #define _ACPI_FAN_H_

+#include <linux/kconfig.h>
+
 #define ACPI_FAN_DEVICE_IDS	\
 	{"INT3404", }, /* Fan */ \
 	{"INTC1044", }, /* Fan for Tiger Lake generation */ \
@@ -56,4 +58,11 @@ struct acpi_fan {
 int acpi_fan_get_fst(struct acpi_device *device, struct acpi_fan_fst *fst);
 int acpi_fan_create_attributes(struct acpi_device *device);
 void acpi_fan_delete_attributes(struct acpi_device *device);
+
+#if IS_REACHABLE(CONFIG_HWMON)
+int devm_acpi_fan_create_hwmon(struct acpi_device *device);
+#else
+static inline int devm_acpi_fan_create_hwmon(struct acpi_device *device) { return 0; };
+#endif
+
 #endif
diff --git a/drivers/acpi/fan_core.c b/drivers/acpi/fan_core.c
index ff72e4ef8738..7cea4495f19b 100644
--- a/drivers/acpi/fan_core.c
+++ b/drivers/acpi/fan_core.c
@@ -336,6 +336,10 @@ static int acpi_fan_probe(struct platform_device *pdev)
 		if (result)
 			return result;

+		result = devm_acpi_fan_create_hwmon(device);
+		if (result)
+			return result;
+
 		result = acpi_fan_create_attributes(device);
 		if (result)
 			return result;
diff --git a/drivers/acpi/fan_hwmon.c b/drivers/acpi/fan_hwmon.c
new file mode 100644
index 000000000000..b01055432ded
--- /dev/null
+++ b/drivers/acpi/fan_hwmon.c
@@ -0,0 +1,83 @@
+// SPDX-License-Identifier: GPL-2.0-or-later
+/*
+ * fan_hwmon.c - hwmon interface for the ACPI Fan driver
+ *
+ * Copyright (C) 2024 Armin Wolf <W_Armin@gmx.de>
+ */
+
+#include <linux/acpi.h>
+#include <linux/hwmon.h>
+#include <linux/limits.h>
+
+#include "fan.h"
+
+/* Returned when the ACPI fan does not support speed reporting */
+#define FAN_SPEED_UNAVAILABLE	0xffffffff
+
+static umode_t acpi_fan_is_visible(const void *drvdata, enum hwmon_sensor_types type, u32 attr,
+				   int channel)
+{
+	return 0444;
+}
+
+static int acpi_fan_read(struct device *dev, enum hwmon_sensor_types type, u32 attr, int channel,
+			 long *val)
+{
+	struct acpi_device *adev = dev_get_drvdata(dev);
+	struct acpi_fan_fst fst;
+	int ret;
+
+	switch (type) {
+	case hwmon_fan:
+		ret = acpi_fan_get_fst(adev, &fst);
+		if (ret < 0)
+			return ret;
+
+		switch (attr) {
+		case hwmon_fan_input:
+			if (fst.speed == FAN_SPEED_UNAVAILABLE)
+				return -ENODATA;
+
+			if (fst.speed > LONG_MAX)
+				return -EOVERFLOW;
+
+			*val = fst.speed;
+			return 0;
+		case hwmon_fan_fault:
+			*val = (fst.speed == FAN_SPEED_UNAVAILABLE);
+			return 0;
+		default:
+			break;
+		}
+		break;
+	default:
+		break;
+	}
+
+	return -EOPNOTSUPP;
+}
+
+static const struct hwmon_ops acpi_fan_ops = {
+	.is_visible = acpi_fan_is_visible,
+	.read = acpi_fan_read,
+};
+
+static const struct hwmon_channel_info * const acpi_fan_info[] = {
+	HWMON_CHANNEL_INFO(fan, HWMON_F_INPUT | HWMON_F_FAULT),
+	NULL
+};
+
+static const struct hwmon_chip_info acpi_fan_chip_info = {
+	.ops = &acpi_fan_ops,
+	.info = acpi_fan_info,
+};
+
+int devm_acpi_fan_create_hwmon(struct acpi_device *device)
+{
+	struct device *hdev;
+
+	hdev = devm_hwmon_device_register_with_info(&device->dev, "acpi_fan", device,
+						    &acpi_fan_chip_info, NULL);
+
+	return PTR_ERR_OR_ZERO(hdev);
+}
--
2.39.2