[PATCH 1/2] hwmon: add fan speed monitoring driver for Surface devices

Ivor Wanders
2023-12-20T23:44:30Z

Adds a driver that provides read only access to the fan speed for Microsoft
Surface Pro devices. The fan speed is always regulated by the EC and cannot
be influenced directly.

Signed-off-by: Ivor Wanders <ivor@iwanders.net>
Link: https://github.com/linux-surface/kernel/pull/144
---
Documentation/hwmon/index.rst | 1 +
Documentation/hwmon/surface_fan.rst | 27 ++++++
MAINTAINERS | 8 ++
drivers/hwmon/Kconfig | 13 +++
drivers/hwmon/Makefile | 1 +
drivers/hwmon/surface_fan.c | 125 ++++++++++++++++++++++++++++
6 files changed, 175 insertions(+)
create mode 100644 Documentation/hwmon/surface_fan.rst
create mode 100644 drivers/hwmon/surface_fan.c

diff --git a/Documentation/hwmon/index.rst b/Documentation/hwmon/index.rst
index 042e1cf95..4dfb3b9bd 100644
--- a/Documentation/hwmon/index.rst
+++ b/Documentation/hwmon/index.rst
@@ -202,6 +202,7 @@ Hardware Monitoring Kernel Drivers
smsc47m1
sparx5-temp
stpddc60
+ surface_fan
sy7636a-hwmon
tc654
tc74
diff --git a/Documentation/hwmon/surface_fan.rst b/Documentation/hwmon/surface_fan.rst
new file mode 100644
index 000000000..6e27a6653
--- /dev/null
+++ b/Documentation/hwmon/surface_fan.rst
@@ -0,0 +1,27 @@
+.. SPDX-License-Identifier: GPL-2.0-or-later
+
+Kernel driver surface_fan
+=========================
+
+Supported Devices:
+
+ * Microsoft Surface Pro 9
+
+Author: Ivor Wanders <ivor@iwanders.net>
+
+Description
+-----------
+
+This provides monitoring of the fan found in some Microsoft Surface Pro devices,
+like the Surface Pro 9. The fan is always controlled by the onboard controller.
+
+Sysfs interface
+---------------
+
+======================= ======= =========================================
+Name Perm Description
+======================= ======= =========================================
+``fan1_input`` RO Current fan speed in RPM.
+``fan1_max`` RO Approximate maximum fan speed.
+``fan1_min`` RO Minimum fan speed used by the controller.
+======================= ======= =========================================
diff --git a/MAINTAINERS b/MAINTAINERS
index 439cf523b..8e7870af3 100644
--- a/MAINTAINERS
+++ b/MAINTAINERS
@@ -14078,6 +14078,14 @@ F: Documentation/driver-api/surface_aggregator/clients/dtx.rst
F: drivers/platform/surface/surface_dtx.c
F: include/uapi/linux/surface_aggregator/dtx.h

+MICROSOFT SURFACE SENSOR FAN DRIVER
+M: Maximilian Luz <luzmaximilian@gmail.com>
+M: Ivor Wanders <ivor@iwanders.net>
+L: linux-hwmon@vger.kernel.org
+S: Maintained
+F: Documentation/hwmon/surface_fan.rst
+F: drivers/hwmon/surface_fan.c
+
MICROSOFT SURFACE GPE LID SUPPORT DRIVER
M: Maximilian Luz <luzmaximilian@gmail.com>
L: platform-driver-x86@vger.kernel.org
diff --git a/drivers/hwmon/Kconfig b/drivers/hwmon/Kconfig
index 307477b8a..4b4d999af 100644
--- a/drivers/hwmon/Kconfig
+++ b/drivers/hwmon/Kconfig
@@ -1965,6 +1965,19 @@ config SENSORS_SMM665
This driver can also be built as a module. If so, the module will
be called smm665.

+config SENSORS_SURFACE_FAN
+ tristate "Surface Fan Driver"
+ depends on SURFACE_AGGREGATOR
+ help
+ Driver that provides monitoring of the fan on Surface Pro devices that
+ have a fan, like the Surface Pro 9.
+
+ This makes the fan's current speed accessible through the hwmon
+ system. It does not provide control over the fan, the firmware is
+ responsible for that, this driver merely provides monitoring.
+
+ Select M or Y here, if you want to be able to read the fan's speed.
+
config SENSORS_ADC128D818
tristate "Texas Instruments ADC128D818"
depends on I2C
diff --git a/drivers/hwmon/Makefile b/drivers/hwmon/Makefile
index 3f4b0fda0..5ae214c06 100644
--- a/drivers/hwmon/Makefile
+++ b/drivers/hwmon/Makefile
@@ -198,6 +198,7 @@ obj-$(CONFIG_SENSORS_SMSC47M1) += smsc47m1.o
obj-$(CONFIG_SENSORS_SMSC47M192)+= smsc47m192.o
obj-$(CONFIG_SENSORS_SPARX5) += sparx5-temp.o
obj-$(CONFIG_SENSORS_STTS751) += stts751.o
+obj-$(CONFIG_SENSORS_SURFACE_FAN)+= surface_fan.o
obj-$(CONFIG_SENSORS_SY7636A) += sy7636a-hwmon.o
obj-$(CONFIG_SENSORS_AMC6821) += amc6821.o
obj-$(CONFIG_SENSORS_TC74) += tc74.o
diff --git a/drivers/hwmon/surface_fan.c b/drivers/hwmon/surface_fan.c
new file mode 100644
index 000000000..7129b25ed
--- /dev/null
+++ b/drivers/hwmon/surface_fan.c
@@ -0,0 +1,125 @@
+// SPDX-License-Identifier: GPL-2.0+
+/*
+ * Surface Fan driver for Surface System Aggregator Module. It provides access
+ * to the fan's rpm through the hwmon system.
+ *
+ * Copyright (C) 2023 Ivor Wanders <ivor@iwanders.net>
+ */
+
+#include <linux/hwmon.h>
+#include <linux/kernel.h>
+#include <linux/module.h>
+#include <linux/platform_device.h>
+#include <linux/surface_aggregator/device.h>
+#include <linux/types.h>
+
+// The minimum speed for the fan when turned on by the controller. The onboard
+// controller uses this as minimum value before turning the fan on or off.
+#define SURFACE_FAN_MIN_SPEED 3000
+// The maximum speed, determined by observation and rounding up to the nearest
+// multiple of 500 to account for variation between individual fans.
+#define SURFACE_FAN_MAX_SPEED 7500
+
+// SSAM
+SSAM_DEFINE_SYNC_REQUEST_CL_R(__ssam_fan_rpm_get, __le16, {
+ .target_category = SSAM_SSH_TC_FAN,
+ .command_id = 0x01,
+});
+
+// hwmon
+umode_t surface_fan_hwmon_is_visible(const void *drvdata,
+ enum hwmon_sensor_types type, u32 attr,
+ int channel)
+{
+ if (type != hwmon_fan)
+ return 0;
+
+ switch (attr) {
+ case hwmon_fan_input:
+ case hwmon_fan_label:
+ case hwmon_fan_min:
+ case hwmon_fan_max:
+ return 0444;
+ default:
+ return 0;
+ }
+}
+
+static int surface_fan_hwmon_read(struct device *dev,
+ enum hwmon_sensor_types type, u32 attr,
+ int channel, long *val)
+{
+ struct ssam_device *sdev = dev_get_drvdata(dev);
+ __le16 value;
+ int res;
+
+ if (type != hwmon_fan)
+ return -EOPNOTSUPP;
+
+ switch (attr) {
+ case hwmon_fan_input:
+ res = __ssam_fan_rpm_get(sdev, &value);
+ if (res)
+ return -EIO;
+ *val = le16_to_cpu(value);
+ return 0;
+ case hwmon_fan_min:
+ *val = SURFACE_FAN_MIN_SPEED;
+ return 0;
+ case hwmon_fan_max:
+ *val = SURFACE_FAN_MAX_SPEED;
+ return 0;
+ default:
+ return -EOPNOTSUPP;
+ }
+}
+
+static const struct hwmon_channel_info *const surface_fan_info[] = {
+ HWMON_CHANNEL_INFO(fan, HWMON_F_INPUT | HWMON_F_MAX | HWMON_F_MIN),
+ NULL
+};
+
+static const struct hwmon_ops surface_fan_hwmon_ops = {
+ .is_visible = surface_fan_hwmon_is_visible,
+ .read = surface_fan_hwmon_read,
+};
+
+static const struct hwmon_chip_info surface_fan_chip_info = {
+ .ops = &surface_fan_hwmon_ops,
+ .info = surface_fan_info,
+};
+
+static int surface_fan_probe(struct ssam_device *sdev)
+{
+ struct device *hdev;
+
+ hdev = devm_hwmon_device_register_with_info(&sdev->dev, "fan", sdev,
+ &surface_fan_chip_info,
+ NULL);
+ if (IS_ERR(hdev))
+ return PTR_ERR(hdev);
+
+ ssam_device_set_drvdata(sdev, sdev);
+
+ return 0;
+}
+
+static const struct ssam_device_id ssam_fan_match[] = {
+ { SSAM_SDEV(FAN, SAM, 0x01, 0x01) },
+ {},
+};
+MODULE_DEVICE_TABLE(ssam, ssam_fan_match);
+
+static struct ssam_device_driver surface_fan = {
+ .probe = surface_fan_probe,
+ .match_table = ssam_fan_match,
+ .driver = {
+ .name = "surface_fan",
+ .probe_type = PROBE_PREFER_ASYNCHRONOUS,
+ },
+};
+module_ssam_device_driver(surface_fan);
+
+MODULE_AUTHOR("Ivor Wanders <ivor@iwanders.net>");
+MODULE_DESCRIPTION("Fan Driver for Surface System Aggregator Module");
+MODULE_LICENSE("GPL");
--
2.17.1