[PATCH v2 0/2] Add JHB100 Fan-Tach support

[PATCH v2 0/2] Add JHB100 Fan-Tach support

[Changhuang Liang]

StarFive Fan-Tach controller can support up to 16 fan tach input.
The series has been tested on the EVB1 board.

Change since v1:
PATCH 1:
- Add explicit minItems/maxItems and range constraints for tach-ch.
- Switch fan node regex to support hex addresses.
- Add pulses-per-revolution demo.
- Rename example node to fan-controller for consistency.
- Limit the reg property to a maximum value of 15
- Fix tach-ch example by changing /bits/ 8 <0x0>, <0x8> to
  /bits/ 8 <0x0 0x8> so both values are parsed as 8-bit cells.

PATCH 2:
- Added hwmon documentation (starfive-fan-tach.rst)
- Added HAS_IOMEM dependency in Kconfig
- Added per-channel pulses-per-revolution DT property (default 2, range 1-4)
- Added mutex and spinlock for proper concurrency protection
- Added armed_stall/armed_slow mechanism to prevent spurious interrupts
- Added retry logic for zero sampling value in rpm read
- Improved probe sequence: clock enable before reset deassert
- Added devm action for remove path cleanup
- Added input validation for write operations
- Added MODULE_DEVICE_TABLE
- Added linux-hwmon mailing list to MAINTAINERS

v1: https://lore.kernel.org/all/20260428082337.743546-1-changhuang.liang@starfivetech.com/

Changhuang Liang (2):
  dt-bindings: hwmon: Add starfive,jhb100-fan-tach
  hwmon: (starfive-fan-tach) Add fan tach driver for StarFive JHB100

 .../hwmon/starfive,jhb100-fan-tach.yaml       |  93 +++
 Documentation/hwmon/index.rst                 |   1 +
 Documentation/hwmon/starfive-fan-tach.rst     |  34 ++
 MAINTAINERS                                   |   8 +
 drivers/hwmon/Kconfig                         |  14 +
 drivers/hwmon/Makefile                        |   1 +
 drivers/hwmon/starfive-fan-tach.c             | 561 ++++++++++++++++++
 7 files changed, 712 insertions(+)
 create mode 100644 Documentation/devicetree/bindings/hwmon/starfive,jhb100-fan-tach.yaml
 create mode 100644 Documentation/hwmon/starfive-fan-tach.rst
 create mode 100644 drivers/hwmon/starfive-fan-tach.c

--
2.25.1

[PATCH v2 1/2] dt-bindings: hwmon: Add starfive,jhb100-fan-tach

[Changhuang Liang]

Add compatible "starfive,jhb100-fan-tach" for StarFive JHB100 Fan-Tach
controller.

Signed-off-by: Changhuang Liang <changhuang.liang@starfivetech.com>
---
 .../hwmon/starfive,jhb100-fan-tach.yaml       | 93 +++++++++++++++++++
 1 file changed, 93 insertions(+)
 create mode 100644 Documentation/devicetree/bindings/hwmon/starfive,jhb100-fan-tach.yaml

diff --git a/Documentation/devicetree/bindings/hwmon/starfive,jhb100-fan-tach.yaml b/Documentation/devicetree/bindings/hwmon/starfive,jhb100-fan-tach.yaml
new file mode 100644
index 000000000000..1dcd4932768f
--- /dev/null
+++ b/Documentation/devicetree/bindings/hwmon/starfive,jhb100-fan-tach.yaml
@@ -0,0 +1,93 @@
+# SPDX-License-Identifier: GPL-2.0-only OR BSD-2-Clause
+%YAML 1.2
+---
+$id: http://devicetree.org/schemas/hwmon/starfive,jhb100-fan-tach.yaml#
+$schema: http://devicetree.org/meta-schemas/core.yaml#
+
+title: StarFive JHB100 Fan-Tach controller
+
+maintainers:
+  - Changhuang Liang <changhuang.liang@starfivetech.com>
+
+description:
+  The StarFive Fan-Tach controller can support up to 16 fan tach input.
+
+properties:
+  compatible:
+    enum:
+      - starfive,jhb100-fan-tach
+
+  reg:
+    maxItems: 1
+
+  clocks:
+    maxItems: 1
+
+  resets:
+    maxItems: 1
+
+  interrupts:
+    maxItems: 1
+
+  "#address-cells":
+    const: 1
+
+  "#size-cells":
+    const: 0
+
+patternProperties:
+  "^fan@[0-9a-f]+$":
+    $ref: fan-common.yaml#
+    unevaluatedProperties: false
+
+    properties:
+      reg:
+        description:
+          PWM channel index. The driver allows two fans to share the same
+          PWM channel, or each fan to use a dedicated channel.
+        maximum: 15
+
+      tach-ch:
+        description:
+          The tachometer channel(s) wired to the fan(s) driven by this PWM
+          channel. Integer values in the range 0-15.
+        minItems: 1
+        maxItems: 2
+        items:
+          maximum: 15
+
+    required:
+      - reg
+      - tach-ch
+
+required:
+  - compatible
+  - reg
+  - clocks
+  - resets
+  - interrupts
+
+additionalProperties: false
+
+examples:
+  - |
+    fan-controller@11be0000 {
+        compatible = "starfive,jhb100-fan-tach";
+        reg = <0x11be0000 0x400>;
+        interrupts = <128>;
+        clocks = <&per2crg 33>;
+        resets = <&per2crg 5>;
+        #address-cells = <1>;
+        #size-cells = <0>;
+
+        fan@0 {
+            reg = <0x0>;
+            tach-ch = /bits/ 8 <0x0 0x8>;
+            pulses-per-revolution = <2>;
+        };
+        fan@1 {
+            reg = <0x1>;
+            tach-ch = /bits/ 8 <0x1>;
+            pulses-per-revolution = <2>;
+        };
+    };
-- 
2.25.1

[PATCH v2 2/2] hwmon: (starfive-fan-tach) Add fan tach driver for StarFive JHB100

[Changhuang Liang]

Add fan tach driver for StarFive JHB100 SoC.

The controller supports up to 16 independent fan tachometer inputs and
reports fan speed in RPM through the hwmon sysfs interface, along with
stall and low-speed alarms.

For this controller, the special clock and reset operation sequence is:
  probe: clk_prepare_enable() than reset_control_deassert()
  remove: clk_disable_unprepare() than reset_control_assert()

Co-developed-by: William Qiu <william.qiu@starfivetech.com>
Signed-off-by: William Qiu <william.qiu@starfivetech.com>
Signed-off-by: Changhuang Liang <changhuang.liang@starfivetech.com>
---
 Documentation/hwmon/index.rst             |   1 +
 Documentation/hwmon/starfive-fan-tach.rst |  34 ++
 MAINTAINERS                               |   8 +
 drivers/hwmon/Kconfig                     |  14 +
 drivers/hwmon/Makefile                    |   1 +
 drivers/hwmon/starfive-fan-tach.c         | 561 ++++++++++++++++++++++
 6 files changed, 619 insertions(+)
 create mode 100644 Documentation/hwmon/starfive-fan-tach.rst
 create mode 100644 drivers/hwmon/starfive-fan-tach.c

diff --git a/Documentation/hwmon/index.rst b/Documentation/hwmon/index.rst
index 29130df44d12..0d64e4cf1051 100644
--- a/Documentation/hwmon/index.rst
+++ b/Documentation/hwmon/index.rst
@@ -253,6 +253,7 @@ Hardware Monitoring Kernel Drivers
    smsc47m1
    sparx5-temp
    spd5118
+   starfive-fan-tach
    stpddc60
    surface_fan
    sy7636a-hwmon
diff --git a/Documentation/hwmon/starfive-fan-tach.rst b/Documentation/hwmon/starfive-fan-tach.rst
new file mode 100644
index 000000000000..5ca03b52ad58
--- /dev/null
+++ b/Documentation/hwmon/starfive-fan-tach.rst
@@ -0,0 +1,34 @@
+.. SPDX-License-Identifier: GPL-2.0
+
+Kernel driver starfive-fan-tach
+===============================
+
+Supported chips:
+
+  * StarFive JHB100
+
+    Prefix: 'starfive_fan_tach'
+
+    Addresses scanned: -
+
+Authors:
+      - Changhuang Liang <changhuang.liang@starfivetech.com>
+
+Description
+-----------
+
+This driver implements support for the fan tachometer controller found on
+the StarFive JHB100 SoC. The controller supports up to 16 independent fan
+tachometer inputs. Each tachometer channel measures the number of pulses
+within a fixed 100 ms window.
+
+Sysfs entries
+-------------
+
+==================== =======================================================
+fan[1-16]_input      Fan speed in RPM (read-only)
+fan[1-16]_min        Lower fan speed limit in RPM (read/write)
+fan[1-16]_enable     Enable/disable the tachometer channel (read/write)
+fan[1-16]_fault      Fan stall indication (read-only)
+fan[1-16]_min_alarm  Fan speed below fan[1-16]_min (read-only)
+==================== =======================================================
diff --git a/MAINTAINERS b/MAINTAINERS
index c545aa121d51..83318d2e3e2e 100644
--- a/MAINTAINERS
+++ b/MAINTAINERS
@@ -25897,6 +25897,14 @@ S:	Supported
 F:	Documentation/devicetree/bindings/interrupt-controller/starfive,jhb100-intc.yaml
 F:	drivers/irqchip/irq-starfive-jhb100-intc.c
 
+STARFIVE JHB100 FAN-TACH DRIVER
+M:	Changhuang Liang <changhuang.liang@starfivetech.com>
+L:	linux-hwmon@vger.kernel.org
+S:	Supported
+F:	Documentation/devicetree/bindings/hwmon/starfive,jhb100-fan-tach.yaml
+F:	Documentation/hwmon/starfive-fan-tach.rst
+F:	drivers/hwmon/starfive-fan-tach.c
+
 STATIC BRANCH/CALL
 M:	Peter Zijlstra <peterz@infradead.org>
 M:	Josh Poimboeuf <jpoimboe@kernel.org>
diff --git a/drivers/hwmon/Kconfig b/drivers/hwmon/Kconfig
index 5c2d3ff5fce8..2c0000f8e777 100644
--- a/drivers/hwmon/Kconfig
+++ b/drivers/hwmon/Kconfig
@@ -2383,6 +2383,20 @@ config SENSORS_SPD5118_DETECT
 
 	  If unsure, say Y.
 
+config SENSORS_STARFIVE_FAN_TACH
+	tristate "StarFive Fan-Tach driver"
+	depends on ARCH_STARFIVE || COMPILE_TEST
+	depends on HAS_IOMEM
+	help
+	  This driver provides support for the fan tachometer controller
+	  found on StarFive SoCs such as the JHB100. The controller supports
+	  up to 16 independent fan tachometer inputs and reports fan speed
+	  in RPM through the hwmon sysfs interface, along with stall and
+	  low-speed alarms.
+
+	  This driver can also be built as a module. If so, the module
+	  will be called starfive-fan-tach.
+
 config SENSORS_TC74
 	tristate "Microchip TC74"
 	depends on I2C
diff --git a/drivers/hwmon/Makefile b/drivers/hwmon/Makefile
index 63effc0ab8d1..80b2704b94e5 100644
--- a/drivers/hwmon/Makefile
+++ b/drivers/hwmon/Makefile
@@ -223,6 +223,7 @@ obj-$(CONFIG_SENSORS_SMSC47M1)	+= smsc47m1.o
 obj-$(CONFIG_SENSORS_SMSC47M192)+= smsc47m192.o
 obj-$(CONFIG_SENSORS_SPARX5)	+= sparx5-temp.o
 obj-$(CONFIG_SENSORS_SPD5118)	+= spd5118.o
+obj-$(CONFIG_SENSORS_STARFIVE_FAN_TACH)	+= starfive-fan-tach.o
 obj-$(CONFIG_SENSORS_STTS751)	+= stts751.o
 obj-$(CONFIG_SENSORS_SURFACE_FAN)+= surface_fan.o
 obj-$(CONFIG_SENSORS_SURFACE_TEMP)+= surface_temp.o
diff --git a/drivers/hwmon/starfive-fan-tach.c b/drivers/hwmon/starfive-fan-tach.c
new file mode 100644
index 000000000000..1e6399db424d
--- /dev/null
+++ b/drivers/hwmon/starfive-fan-tach.c
@@ -0,0 +1,561 @@
+// SPDX-License-Identifier: GPL-2.0
+/*
+ * FAN-TACH controller driver for StarFive JHB100
+ *
+ * Copyright (C) 2018-2026 StarFive Technology Co., Ltd.
+ */
+
+#include <linux/bitfield.h>
+#include <linux/clk.h>
+#include <linux/completion.h>
+#include <linux/delay.h>
+#include <linux/errno.h>
+#include <linux/hwmon.h>
+#include <linux/interrupt.h>
+#include <linux/io.h>
+#include <linux/iopoll.h>
+#include <linux/jiffies.h>
+#include <linux/kernel.h>
+#include <linux/math64.h>
+#include <linux/module.h>
+#include <linux/mutex.h>
+#include <linux/of.h>
+#include <linux/platform_device.h>
+#include <linux/reset.h>
+#include <linux/spinlock.h>
+
+#define STARFIVE_FAN_TACH_CH			16
+
+/* Fan-tach register offest */
+#define STARFIVE_FAN_TACH_STATUS		0x0c
+
+#define STARFIVE_FAN_TACH_SPEED(ch)		(((ch) * 0x04) + 0x10)
+#define STARFIVE_FAN_TACH_SPEED_VALID		BIT(31)
+#define STARFIVE_FAN_TACH_VALUE_MASK		GENMASK(30, 0)
+
+#define STARFIVE_FAN_TACH_THRESHOLD(ch)		(((ch) * 0x04) + 0x50)
+
+#define STARFIVE_FAN_TACH_INT_EN		0x90
+#define STARFIVE_FAN_TACH_STALL_INT_MASK	GENMASK(15, 0)
+#define STARFIVE_FAN_TACH_SLOW_INT_MASK		GENMASK(31, 16)
+#define STARFIVE_FAN_TACH_STALL_INT(ch)		BIT(ch)
+#define STARFIVE_FAN_TACH_SLOW_INT(ch)		(BIT(ch) << 16)
+
+#define STARFIVE_FAN_TACH_MEASURE_TIME		0x94
+
+#define STARFIVE_FAN_TACH_CH_EN			0x98
+#define STARFIVE_FAN_TACH_EN(ch)		BIT(ch)
+
+#define STARFIVE_FAN_DEFAULT_PULSE_PR		2
+#define STARFIVE_FAN_DEFAULT_MEASURE_RATIO	10
+#define STARFIVE_FAN_DEFAULT_RPM_PAUSE_TIME	(60 * STARFIVE_FAN_DEFAULT_MEASURE_RATIO)
+
+#define STARFIVE_FAN_TACH_TIMEOUT \
+	(USEC_PER_SEC / STARFIVE_FAN_DEFAULT_MEASURE_RATIO)
+
+#define STARFIVE_FAN_TACH_TIMEOUT_JIFFIES \
+	(msecs_to_jiffies(1000) / STARFIVE_FAN_DEFAULT_MEASURE_RATIO)
+
+#define FAN_ATTRIBUTE_SET \
+	(HWMON_F_INPUT | HWMON_F_MIN | HWMON_F_ENABLE | \
+	 HWMON_F_FAULT | HWMON_F_MIN_ALARM)
+
+struct starfive_fan_tach_data {
+	struct device *dev;
+	/*
+	 * Serialises the read-modify-write sequences on CH_EN and INT_EN,
+	 * and the arm/disarm window of the fault/min_alarm read paths.
+	 */
+	struct mutex lock;
+	void __iomem *regs;
+	struct reset_control *rst;
+	struct clk *clk;
+	bool tach_present[STARFIVE_FAN_TACH_CH];
+	unsigned long clk_rate; /* APB clock frequency */
+	u8 pulses_per_rev[STARFIVE_FAN_TACH_CH];
+	struct completion comp_stall[STARFIVE_FAN_TACH_CH];
+	struct completion comp_slow[STARFIVE_FAN_TACH_CH];
+	u8 fan_stall[STARFIVE_FAN_TACH_CH];
+	u8 fan_slow[STARFIVE_FAN_TACH_CH];
+	u32 armed_stall;
+	u32 armed_slow;
+	/* protects fan_stall[]/fan_slow[]/armed_* and the STATUS register */
+	spinlock_t irq_lock;
+};
+
+static void starfive_fan_tach_ch_enable(struct starfive_fan_tach_data *priv, u8 tach_ch,
+					bool enable)
+{
+	if (enable) {
+		writel(readl(priv->regs + STARFIVE_FAN_TACH_CH_EN) |
+		       STARFIVE_FAN_TACH_EN(tach_ch),
+		       priv->regs + STARFIVE_FAN_TACH_CH_EN);
+	} else {
+		writel(readl(priv->regs + STARFIVE_FAN_TACH_CH_EN) &
+		       ~(STARFIVE_FAN_TACH_EN(tach_ch)),
+		       priv->regs + STARFIVE_FAN_TACH_CH_EN);
+	}
+}
+
+static void starfive_fan_tach_ch_stall_unmask(struct starfive_fan_tach_data *priv, u8 tach_ch,
+					      bool unmask)
+{
+	if (unmask) {
+		writel(readl(priv->regs + STARFIVE_FAN_TACH_INT_EN) |
+		       STARFIVE_FAN_TACH_STALL_INT(tach_ch),
+		       priv->regs + STARFIVE_FAN_TACH_INT_EN);
+	} else {
+		writel(readl(priv->regs + STARFIVE_FAN_TACH_INT_EN) &
+		       ~STARFIVE_FAN_TACH_STALL_INT(tach_ch),
+		       priv->regs + STARFIVE_FAN_TACH_INT_EN);
+	}
+}
+
+static void starfive_fan_tach_ch_slow_unmask(struct starfive_fan_tach_data *priv, u8 tach_ch,
+					     bool unmask)
+{
+	if (unmask) {
+		writel(readl(priv->regs + STARFIVE_FAN_TACH_INT_EN) |
+		       STARFIVE_FAN_TACH_SLOW_INT(tach_ch),
+		       priv->regs + STARFIVE_FAN_TACH_INT_EN);
+	} else {
+		writel(readl(priv->regs + STARFIVE_FAN_TACH_INT_EN) &
+		       ~STARFIVE_FAN_TACH_SLOW_INT(tach_ch),
+		       priv->regs + STARFIVE_FAN_TACH_INT_EN);
+	}
+}
+
+static u32 starfive_fan_tach_rpm_to_val(struct starfive_fan_tach_data *priv, u8 tach_ch, u32 rpm)
+{
+	u64 tach_val;
+	u8 ppr;
+
+	ppr = priv->pulses_per_rev[tach_ch];
+
+	tach_val = (u64)rpm * ppr;
+	tach_val = div_u64(tach_val, STARFIVE_FAN_DEFAULT_RPM_PAUSE_TIME);
+
+	return min_t(u64, tach_val, STARFIVE_FAN_TACH_VALUE_MASK);
+}
+
+static long starfive_fan_tach_val_to_rpm(struct starfive_fan_tach_data *priv, u8 tach_ch,
+					 u32 tach_val)
+{
+	u64 rpm;
+	u8 ppr;
+
+	ppr = priv->pulses_per_rev[tach_ch];
+
+	rpm = (u64)tach_val * STARFIVE_FAN_DEFAULT_RPM_PAUSE_TIME;
+
+	return div_u64(rpm, ppr);
+}
+
+static int starfive_fan_tach_get_rpm(struct starfive_fan_tach_data *priv,
+				     u8 tach_ch, long *rpm)
+{
+	u32 val;
+	int ret;
+
+	ret = readl_poll_timeout(priv->regs + STARFIVE_FAN_TACH_SPEED(tach_ch),
+				 val, val & STARFIVE_FAN_TACH_SPEED_VALID,
+				 100, STARFIVE_FAN_TACH_TIMEOUT);
+	if (ret)
+		return -ENODATA;
+
+	val = FIELD_GET(STARFIVE_FAN_TACH_VALUE_MASK, val);
+	if (!val) {
+		/* Sampling = 0 may mean no valid capture; wait 1.5 more cycles for valid read. */
+		fsleep(STARFIVE_FAN_TACH_TIMEOUT + STARFIVE_FAN_TACH_TIMEOUT / 2);
+		ret = readl_poll_timeout(priv->regs + STARFIVE_FAN_TACH_SPEED(tach_ch),
+					 val, val & STARFIVE_FAN_TACH_SPEED_VALID,
+					 100, STARFIVE_FAN_TACH_TIMEOUT);
+		if (ret)
+			return -ENODATA;
+
+		val = FIELD_GET(STARFIVE_FAN_TACH_VALUE_MASK, val);
+	}
+
+	*rpm = starfive_fan_tach_val_to_rpm(priv, tach_ch, val);
+
+	return 0;
+}
+
+static long starfive_fan_tach_get_rpm_threshold(struct starfive_fan_tach_data *priv,
+						u8 tach_ch)
+{
+	u32 val;
+
+	val = readl(priv->regs + STARFIVE_FAN_TACH_THRESHOLD(tach_ch));
+
+	val = FIELD_GET(STARFIVE_FAN_TACH_VALUE_MASK, val);
+
+	return starfive_fan_tach_val_to_rpm(priv, tach_ch, val);
+}
+
+static void starfive_set_tach_rpm_threshold(struct starfive_fan_tach_data *priv,
+					    u8 tach_ch, u32 val)
+{
+	u32 reg_val;
+
+	reg_val = starfive_fan_tach_rpm_to_val(priv, tach_ch, val);
+	reg_val = clamp_val(reg_val, 1, STARFIVE_FAN_TACH_VALUE_MASK);
+
+	writel(reg_val, priv->regs + STARFIVE_FAN_TACH_THRESHOLD(tach_ch));
+}
+
+static int starfive_fan_tach_get_ch_en(struct starfive_fan_tach_data *priv,
+				       u8 tach_ch)
+{
+	u32 enable;
+
+	enable = readl(priv->regs + STARFIVE_FAN_TACH_CH_EN);
+
+	return (enable & (1 << tach_ch)) ? 1 : 0;
+}
+
+static int starfive_fan_tach_hwmon_read(struct device *dev,
+					enum hwmon_sensor_types type, u32 attr,
+					int channel, long *val)
+{
+	struct starfive_fan_tach_data *priv = dev_get_drvdata(dev);
+	int ret = 0;
+
+	switch (attr) {
+	case hwmon_fan_fault:
+		scoped_guard(mutex, &priv->lock) {
+			scoped_guard(spinlock_irqsave, &priv->irq_lock) {
+				writel(STARFIVE_FAN_TACH_STALL_INT(channel),
+				       priv->regs + STARFIVE_FAN_TACH_STATUS);
+				/* clear fan_stall first */
+				priv->fan_stall[channel] = 0;
+				reinit_completion(&priv->comp_stall[channel]);
+				priv->armed_stall |= BIT(channel);
+			}
+
+			starfive_fan_tach_ch_stall_unmask(priv, channel, true);
+
+			/* Waiting for hardware to measure */
+			wait_for_completion_timeout(&priv->comp_stall[channel],
+						    2 * STARFIVE_FAN_TACH_TIMEOUT_JIFFIES);
+
+			starfive_fan_tach_ch_stall_unmask(priv, channel, false);
+
+			scoped_guard(spinlock_irqsave, &priv->irq_lock) {
+				priv->armed_stall &= ~BIT(channel);
+				*val = priv->fan_stall[channel];
+			}
+		}
+
+		break;
+	case hwmon_fan_input:
+		ret = starfive_fan_tach_get_ch_en(priv, channel);
+		if (!ret)
+			return -ENODATA;
+
+		ret = starfive_fan_tach_get_rpm(priv, channel, val);
+		if (ret < 0)
+			return ret;
+
+		break;
+	case hwmon_fan_min:
+		*val = starfive_fan_tach_get_rpm_threshold(priv, channel);
+
+		break;
+	case hwmon_fan_min_alarm:
+		scoped_guard(mutex, &priv->lock) {
+			scoped_guard(spinlock_irqsave, &priv->irq_lock) {
+				writel(STARFIVE_FAN_TACH_SLOW_INT(channel),
+				       priv->regs + STARFIVE_FAN_TACH_STATUS);
+				/* clear fan_slow first */
+				priv->fan_slow[channel] = 0;
+				reinit_completion(&priv->comp_slow[channel]);
+				priv->armed_slow |= BIT(channel);
+			}
+
+			starfive_fan_tach_ch_slow_unmask(priv, channel, true);
+
+			/* Waiting for hardware to measure */
+			wait_for_completion_timeout(&priv->comp_slow[channel],
+						    2 * STARFIVE_FAN_TACH_TIMEOUT_JIFFIES);
+
+			starfive_fan_tach_ch_slow_unmask(priv, channel, false);
+
+			scoped_guard(spinlock_irqsave, &priv->irq_lock) {
+				priv->armed_slow &= ~BIT(channel);
+				*val = priv->fan_slow[channel];
+			}
+		}
+
+		break;
+	case hwmon_fan_enable:
+		*val = starfive_fan_tach_get_ch_en(priv, channel);
+
+		break;
+	default:
+		return -EOPNOTSUPP;
+	}
+
+	return 0;
+}
+
+static int starfive_fan_tach_hwmon_write(struct device *dev,
+					 enum hwmon_sensor_types type, u32 attr,
+					 int channel, long val)
+{
+	struct starfive_fan_tach_data *priv = dev_get_drvdata(dev);
+
+	guard(mutex)(&priv->lock);
+
+	switch (attr) {
+	case hwmon_fan_min:
+		if (val < 0 || val > U32_MAX)
+			return -EINVAL;
+
+		starfive_set_tach_rpm_threshold(priv, channel, val);
+		break;
+	case hwmon_fan_enable:
+		if (val != 0 && val != 1)
+			return -EINVAL;
+
+		starfive_fan_tach_ch_enable(priv, channel, val);
+		break;
+	default:
+		return -EOPNOTSUPP;
+	}
+
+	return 0;
+}
+
+static umode_t starfive_fan_tach_dev_is_visible(const void *drvdata,
+						enum hwmon_sensor_types type,
+						u32 attr, int channel)
+{
+	const struct starfive_fan_tach_data *priv = drvdata;
+
+	if (!priv->tach_present[channel])
+		return 0;
+
+	switch (attr) {
+	case hwmon_fan_input:
+	case hwmon_fan_fault:
+	case hwmon_fan_min_alarm:
+		return 0444;
+	case hwmon_fan_min:
+	case hwmon_fan_enable:
+		return 0644;
+	}
+
+	return 0;
+}
+
+static const struct hwmon_ops starfive_fan_tach_ops = {
+	.is_visible = starfive_fan_tach_dev_is_visible,
+	.read = starfive_fan_tach_hwmon_read,
+	.write = starfive_fan_tach_hwmon_write
+};
+
+static const struct hwmon_channel_info *starfive_fan_tach_info[] = {
+	HWMON_CHANNEL_INFO(fan,
+			   FAN_ATTRIBUTE_SET, FAN_ATTRIBUTE_SET,
+			   FAN_ATTRIBUTE_SET, FAN_ATTRIBUTE_SET,
+			   FAN_ATTRIBUTE_SET, FAN_ATTRIBUTE_SET,
+			   FAN_ATTRIBUTE_SET, FAN_ATTRIBUTE_SET,
+			   FAN_ATTRIBUTE_SET, FAN_ATTRIBUTE_SET,
+			   FAN_ATTRIBUTE_SET, FAN_ATTRIBUTE_SET,
+			   FAN_ATTRIBUTE_SET, FAN_ATTRIBUTE_SET,
+			   FAN_ATTRIBUTE_SET, FAN_ATTRIBUTE_SET),
+	NULL
+};
+
+static const struct hwmon_chip_info starfive_fan_tach_chip_info = {
+	.ops = &starfive_fan_tach_ops,
+	.info = starfive_fan_tach_info,
+};
+
+static int starfive_fan_tach_create_fan(struct device *dev, struct device_node *child,
+					struct starfive_fan_tach_data *priv)
+{
+	u8 tach_ch[STARFIVE_FAN_TACH_CH];
+	int ret, count;
+	u32 ppr, index;
+
+	count = of_property_count_u8_elems(child, "tach-ch");
+	if (count < 1 || count > STARFIVE_FAN_TACH_CH)
+		return -EINVAL;
+
+	ret = of_property_read_u8_array(child, "tach-ch", tach_ch, count);
+	if (ret)
+		return ret;
+
+	/* Parse pulses-per-revolution, default to 2 if not specified */
+	ppr = STARFIVE_FAN_DEFAULT_PULSE_PR;
+	of_property_read_u32(child, "pulses-per-revolution", &ppr);
+
+	if (!ppr || ppr > 4) {
+		dev_err(dev, "Invalid pulses-per-revolution %u, must be 1-4\n", ppr);
+		return -EINVAL;
+	}
+
+	for (index = 0; index < count; index++) {
+		u8 ch = tach_ch[index];
+
+		if (ch >= STARFIVE_FAN_TACH_CH) {
+			dev_warn(priv->dev, "Invalid tach-ch %d, skipping\n", ch);
+			continue;
+		}
+
+		priv->pulses_per_rev[ch] = ppr;
+		priv->tach_present[ch] = true;
+		starfive_fan_tach_ch_enable(priv, ch, true);
+	}
+
+	return 0;
+}
+
+static irqreturn_t starfive_fan_tach_irq(int irq, void *dev_id)
+{
+	struct starfive_fan_tach_data *priv = dev_id;
+	u32 fan_status;
+	int i;
+
+	guard(spinlock)(&priv->irq_lock);
+
+	fan_status = readl(priv->regs + STARFIVE_FAN_TACH_STATUS);
+	if (!fan_status)
+		return IRQ_NONE;
+
+	writel(fan_status, priv->regs + STARFIVE_FAN_TACH_STATUS);
+
+	for (i = 0; i < STARFIVE_FAN_TACH_CH; i++) {
+		if (!priv->tach_present[i])
+			continue;
+
+		if ((fan_status & STARFIVE_FAN_TACH_STALL_INT(i)) &&
+		    (priv->armed_stall & BIT(i))) {
+			priv->fan_stall[i] = 1;
+			complete(&priv->comp_stall[i]);
+		}
+
+		if ((fan_status & STARFIVE_FAN_TACH_SLOW_INT(i)) &&
+		    (priv->armed_slow & BIT(i))) {
+			priv->fan_slow[i] = 1;
+			complete(&priv->comp_slow[i]);
+		}
+	}
+
+	return IRQ_HANDLED;
+}
+
+static void starfive_fan_tach_disable(void *data)
+{
+	struct starfive_fan_tach_data *priv = data;
+
+	clk_disable_unprepare(priv->clk);
+	reset_control_assert(priv->rst);
+}
+
+static int starfive_fan_tach_probe(struct platform_device *pdev)
+{
+	struct device *hwmon_dev, *dev = &pdev->dev;
+	struct starfive_fan_tach_data *priv;
+	int irq;
+	int ret;
+	u32 i;
+
+	priv = devm_kzalloc(dev, sizeof(*priv), GFP_KERNEL);
+	if (!priv)
+		return -ENOMEM;
+
+	priv->dev = dev;
+	spin_lock_init(&priv->irq_lock);
+
+	for (i = 0; i < STARFIVE_FAN_TACH_CH; i++) {
+		init_completion(&priv->comp_stall[i]);
+		init_completion(&priv->comp_slow[i]);
+	}
+
+	priv->regs = devm_platform_ioremap_resource(pdev, 0);
+	if (IS_ERR(priv->regs))
+		return dev_err_probe(dev, PTR_ERR(priv->regs),
+				     "Unable to map IO resources\n");
+
+	priv->clk = devm_clk_get(dev, NULL);
+	if (IS_ERR(priv->clk))
+		return dev_err_probe(dev, PTR_ERR(priv->clk),
+				     "Unable to get fan tach's clock\n");
+
+	priv->rst = devm_reset_control_get_exclusive(dev, NULL);
+	if (IS_ERR(priv->rst))
+		return dev_err_probe(dev, PTR_ERR(priv->rst),
+				     "Unable to get fan tach's reset\n");
+
+	ret = clk_prepare_enable(priv->clk);
+	if (ret)
+		return dev_err_probe(dev, ret, "Failed to enable clock\n");
+
+	priv->clk_rate = clk_get_rate(priv->clk);
+	if (!priv->clk_rate) {
+		clk_disable_unprepare(priv->clk);
+		return dev_err_probe(dev, -EINVAL, "Unable to get clock's rate\n");
+	}
+
+	ret = reset_control_deassert(priv->rst);
+	if (ret) {
+		clk_disable_unprepare(priv->clk);
+		return dev_err_probe(dev, ret, "Failed to deassert reset\n");
+	}
+
+	ret = devm_add_action_or_reset(dev, starfive_fan_tach_disable, priv);
+	if (ret)
+		return ret;
+
+	ret = devm_mutex_init(dev, &priv->lock);
+	if (ret)
+		return ret;
+
+	writel(STARFIVE_FAN_TACH_STALL_INT_MASK | STARFIVE_FAN_TACH_SLOW_INT_MASK,
+	       priv->regs + STARFIVE_FAN_TACH_STATUS);
+	writel(priv->clk_rate / STARFIVE_FAN_DEFAULT_MEASURE_RATIO,
+	       priv->regs + STARFIVE_FAN_TACH_MEASURE_TIME);
+
+	for_each_child_of_node_scoped(dev->of_node, child) {
+		ret = starfive_fan_tach_create_fan(dev, child, priv);
+		if (ret)
+			return dev_err_probe(dev, ret, "Failed to create fan %pOF\n", child);
+	}
+
+	irq = platform_get_irq(pdev, 0);
+	if (irq < 0)
+		return dev_err_probe(dev, irq, "Failed to get IRQ\n");
+
+	ret = devm_request_irq(dev, irq, starfive_fan_tach_irq, 0, pdev->name, priv);
+	if (ret)
+		return ret;
+
+	hwmon_dev = devm_hwmon_device_register_with_info(dev, "starfive_fan_tach",
+							 priv, &starfive_fan_tach_chip_info,
+							 NULL);
+	return PTR_ERR_OR_ZERO(hwmon_dev);
+}
+
+static const struct of_device_id starfive_fan_tach_of_match[] = {
+	{ .compatible = "starfive,jhb100-fan-tach", },
+	{ /* sentinel */ }
+};
+MODULE_DEVICE_TABLE(of, starfive_fan_tach_of_match);
+
+static struct platform_driver starfive_fan_tach_driver = {
+	.probe = starfive_fan_tach_probe,
+	.driver	= {
+		.name = "starfive-fan-tach",
+		.of_match_table = starfive_fan_tach_of_match,
+	},
+};
+
+module_platform_driver(starfive_fan_tach_driver);
+
+MODULE_AUTHOR("William Qiu <william.qiu@starfivetech.com>");
+MODULE_AUTHOR("Changhuang Liang <changhuang.liang@starfivetech.com>");
+MODULE_DESCRIPTION("StarFive JHB100 Fan Tach device driver");
+MODULE_LICENSE("GPL");
-- 
2.25.1

Re: [PATCH v2 1/2] dt-bindings: hwmon: Add starfive,jhb100-fan-tach

[sashiko-bot]

> Add compatible "starfive,jhb100-fan-tach" for StarFive JHB100 Fan-Tach
> controller.
> 
> Signed-off-by: Changhuang Liang <changhuang.liang@starfivetech.com>

Sashiko has reviewed this patch and found no issues. It looks great!

-- 
Sashiko AI review · https://sashiko.dev/#/patchset/20260819091601.41077-1-changhuang.liang@starfivetech.com?part=1

Re: [PATCH v2 2/2] hwmon: (starfive-fan-tach) Add fan tach driver for StarFive JHB100

[sashiko-bot]

Thank you for your contribution! Sashiko AI review found 1 potential issue(s) to consider:
- [Medium] Alarm attributes violate the hwmon ABI (sticky semantics) and hold a global mutex across a 200ms sleep, forcing strict serialization and massive latency.
--

--- Patch [2]: [PATCH v2 2/2] hwmon: (starfive-fan-tach) Add fan tach driver for StarFive JHB100 ---
commit f832cfa14cd6c4c786efa0a34afc865eca6dcf71
Author: Changhuang Liang <changhuang.liang@starfivetech.com>
Subject: hwmon: (starfive-fan-tach) Add fan tach driver for StarFive JHB100

This commit adds a fan tachometer driver for the StarFive JHB100 SoC. It
supports up to 16 independent fan tachometer inputs and reports fan speed,
stall, and low-speed alarms through the hwmon sysfs interface.

> diff --git a/drivers/hwmon/starfive-fan-tach.c b/drivers/hwmon/starfive-fan-tach.c
> new file mode 100644
> index 0000000000000..1e6399db424dc
> --- /dev/null
> +++ b/drivers/hwmon/starfive-fan-tach.c

[ ... ]

> +static int starfive_fan_tach_hwmon_read(struct device *dev,
> +					enum hwmon_sensor_types type, u32 attr,
> +					int channel, long *val)
> +{
> +	struct starfive_fan_tach_data *priv = dev_get_drvdata(dev);
> +	int ret = 0;
> +
> +	switch (attr) {
> +	case hwmon_fan_fault:
> +		scoped_guard(mutex, &priv->lock) {
> +			scoped_guard(spinlock_irqsave, &priv->irq_lock) {
> +				writel(STARFIVE_FAN_TACH_STALL_INT(channel),
> +				       priv->regs + STARFIVE_FAN_TACH_STATUS);
> +				/* clear fan_stall first */
> +				priv->fan_stall[channel] = 0;
> +				reinit_completion(&priv->comp_stall[channel]);
> +				priv->armed_stall |= BIT(channel);
> +			}
> +
> +			starfive_fan_tach_ch_stall_unmask(priv, channel, true);
> +
> +			/* Waiting for hardware to measure */
> +			wait_for_completion_timeout(&priv->comp_stall[channel],
> +						    2 * STARFIVE_FAN_TACH_TIMEOUT_JIFFIES);

[Severity: Medium]
Does reading the fault attribute violate the hwmon ABI by blocking to poll the
hardware instead of returning instantaneous sticky status?

Also, because wait_for_completion_timeout() is called inside
scoped_guard(mutex, &priv->lock), doesn't this hold the global mutex across a
200ms sleep?

If a user tool (like sensors) sequentially reads the alarms for all 16 channels,
could this stall the reader for over 6 seconds and block all other concurrent
reads/writes to this device?

[ ... ]

> +	case hwmon_fan_min_alarm:
> +		scoped_guard(mutex, &priv->lock) {
> +			scoped_guard(spinlock_irqsave, &priv->irq_lock) {
> +				writel(STARFIVE_FAN_TACH_SLOW_INT(channel),
> +				       priv->regs + STARFIVE_FAN_TACH_STATUS);
> +				/* clear fan_slow first */
> +				priv->fan_slow[channel] = 0;
> +				reinit_completion(&priv->comp_slow[channel]);
> +				priv->armed_slow |= BIT(channel);
> +			}
> +
> +			starfive_fan_tach_ch_slow_unmask(priv, channel, true);
> +
> +			/* Waiting for hardware to measure */
> +			wait_for_completion_timeout(&priv->comp_slow[channel],
> +						    2 * STARFIVE_FAN_TACH_TIMEOUT_JIFFIES);

[Severity: Medium]
Similar to the fault attribute above, does reading the min_alarm attribute
violate the hwmon ABI by blocking instead of returning a sticky status?

Does holding the global mutex during this sleep similarly risk blocking
concurrent device accesses and causing long stalls when reading multiple
channels?

-- 
Sashiko AI review · https://sashiko.dev/#/patchset/20260819091601.41077-1-changhuang.liang@starfivetech.com?part=2