[PATCH v2 2/3] thermal: hwmon: Register a hwmon device for each thermal zone

["Rafael J. Wysocki" <rafael@kernel.org>]

From: Rafael J. Wysocki <rafael.j.wysocki@intel.com>

The current code creates one hwmon device per thermal zone type and that
device is registered under the first thermal zone of the given type.

That turns out to be problematic when the thermal zone holding the
hwmon device is removed.

For example, say that there are two ACPI thermal zones on a system

/sys/devices/virtual/thermal/thermal_zone0/
/sys/devices/virtual/thermal/thermal_zone1/

The current code registers a hwmon class device for thermal_zone0 only:

/sys/devices/virtual/thermal/thermal_zone0/hwmon0/

because the type is "acpitz" for both of them, but it adds a sysfs
attribute that belongs to thermal_zone1 under it:

/sys/devices/virtual/thermal/thermal_zone0/hwmon0/temp2_input

There is also

/sys/devices/virtual/thermal/thermal_zone0/hwmon0/temp1_input

which belongs to thermal_zone0.

When thermal_zone0 is removed, say because the ACPI thermal driver is
unbound from the underlying platform device, the removal code skips the
removal of hwmon0 because of the temp2_input attribute belonging to
thermal_zone1 which effectively prevents thermal_zone0 removal from
making progress.

To address this problem, rework the thermal hwmon code to register one
hwmon device for each thermal zone, but since user space utilities
produce confusing output in some cases when there are multiple hwmon
devices with the same name attribute value present under thermal zones
of the same type, append the thermal zone ID preceded by an underline
character to the name of the hwmon device registered for that thermal
zone.

Link: https://lore.kernel.org/linux-pm/20260402021828.16556-1-liujia6264@gmail.com/
Fixes: f6b6b52ef7a5 ("thermal_hwmon: Pass the originating device down to hwmon_device_register_with_info")
Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com>
---

v1 -> v2:
   * Rebase on top of [1/3]
   * Subject update
   * Introduce THERMAL_HWMON_NAME_LENGTH (for hwmon device name attribute
     values) and avoid the truncation of thermal zone type when creating
     those attributes (sashiko.dev)
   * Drop hwmon_node (not necessary any more) from struct thermal_hwmon_temp
     (sashiko.dev)
   * Avoid mixing scoped_guard() with gotos in thermal_add_hwmon_sysfs()
     (sashiko.dev)

---

The reason why I have decided to take this approach is because it allows
the code to be simplified subsequently by using regular extra_groups for
hwmon instead of adding device attributes directly (see the next patch)
and going back to the state before commit f6b6b52ef7a5 is seriously
unattractive.  However, if it breaks user space for people, there really
won't be much choice.

---
 drivers/thermal/thermal_hwmon.c |  151 ++++++++++++----------------------------
 1 file changed, 47 insertions(+), 104 deletions(-)

--- a/drivers/thermal/thermal_hwmon.c
+++ b/drivers/thermal/thermal_hwmon.c
@@ -19,30 +19,33 @@
 #include "thermal_hwmon.h"
 #include "thermal_core.h"
 
-/* hwmon sys I/F */
-/* thermal zone devices with the same type share one hwmon device */
-struct thermal_hwmon_device {
-	char type[THERMAL_NAME_LENGTH];
-	struct device *device;
-	int count;
-	struct list_head tz_list;
-	struct list_head node;
-};
+/*
+ * Needs to be large enough to hold a thermal zone type string followed by an
+ * underline character and a 32-bit integer in decimal representation.
+ */
+#define THERMAL_HWMON_NAME_LENGTH (THERMAL_NAME_LENGTH + 11)
 
 struct thermal_hwmon_attr {
 	struct device_attribute attr;
-	char name[16];
 };
 
 /* one temperature input for each thermal zone */
 struct thermal_hwmon_temp {
-	struct list_head hwmon_node;
 	struct thermal_zone_device *tz;
 	struct thermal_hwmon_attr temp_input;	/* hwmon sys attr */
 	struct thermal_hwmon_attr temp_crit;	/* hwmon sys attr */
 	bool temp_crit_present;
 };
 
+/* hwmon sys I/F */
+/* thermal zone devices with the same type share one hwmon device */
+struct thermal_hwmon_device {
+	char name[THERMAL_HWMON_NAME_LENGTH];
+	struct device *device;
+	struct list_head node;
+	struct thermal_hwmon_temp tz_temp;
+};
+
 static LIST_HEAD(thermal_hwmon_list);
 
 static DEFINE_MUTEX(thermal_hwmon_list_lock);
@@ -88,45 +91,6 @@ temp_crit_show(struct device *dev, struc
 	return sysfs_emit(buf, "%d\n", temperature);
 }
 
-
-static struct thermal_hwmon_device *
-thermal_hwmon_lookup_by_type(const struct thermal_zone_device *tz)
-{
-	struct thermal_hwmon_device *hwmon;
-	char type[THERMAL_NAME_LENGTH];
-
-	mutex_lock(&thermal_hwmon_list_lock);
-	list_for_each_entry(hwmon, &thermal_hwmon_list, node) {
-		strscpy(type, tz->type);
-		strreplace(type, '-', '_');
-		if (!strcmp(hwmon->type, type)) {
-			mutex_unlock(&thermal_hwmon_list_lock);
-			return hwmon;
-		}
-	}
-	mutex_unlock(&thermal_hwmon_list_lock);
-
-	return NULL;
-}
-
-/* Find the temperature input matching a given thermal zone */
-static struct thermal_hwmon_temp *
-thermal_hwmon_lookup_temp(const struct thermal_hwmon_device *hwmon,
-			  const struct thermal_zone_device *tz)
-{
-	struct thermal_hwmon_temp *temp;
-
-	mutex_lock(&thermal_hwmon_list_lock);
-	list_for_each_entry(temp, &hwmon->tz_list, hwmon_node)
-		if (temp->tz == tz) {
-			mutex_unlock(&thermal_hwmon_list_lock);
-			return temp;
-		}
-	mutex_unlock(&thermal_hwmon_list_lock);
-
-	return NULL;
-}
-
 static bool thermal_zone_crit_temp_valid(struct thermal_zone_device *tz)
 {
 	int temp;
@@ -137,54 +101,39 @@ int thermal_add_hwmon_sysfs(struct therm
 {
 	struct thermal_hwmon_device *hwmon;
 	struct thermal_hwmon_temp *temp;
-	int new_hwmon_device = 1;
 	int result;
 
-	hwmon = thermal_hwmon_lookup_by_type(tz);
-	if (hwmon) {
-		new_hwmon_device = 0;
-		goto register_sys_interface;
-	}
-
 	hwmon = kzalloc_obj(*hwmon);
 	if (!hwmon)
 		return -ENOMEM;
 
-	INIT_LIST_HEAD(&hwmon->tz_list);
-	strscpy(hwmon->type, tz->type, THERMAL_NAME_LENGTH);
-	strreplace(hwmon->type, '-', '_');
+	/*
+	 * Append the thermal zone ID preceded by an underline character to the
+	 * type to disambiguate the sensors command output.
+	 */
+	scnprintf(hwmon->name, THERMAL_HWMON_NAME_LENGTH, "%s_%d", tz->type, tz->id);
+	strreplace(hwmon->name, '-', '_');
 	hwmon->device = hwmon_device_register_for_thermal(&tz->device,
-							  hwmon->type, hwmon);
+							  hwmon->name, hwmon);
 	if (IS_ERR(hwmon->device)) {
 		result = PTR_ERR(hwmon->device);
 		goto free_mem;
 	}
 
- register_sys_interface:
-	temp = kzalloc_obj(*temp);
-	if (!temp) {
-		result = -ENOMEM;
-		goto unregister_name;
-	}
+	temp = &hwmon->tz_temp;
 
 	temp->tz = tz;
-	hwmon->count++;
 
-	snprintf(temp->temp_input.name, sizeof(temp->temp_input.name),
-		 "temp%d_input", hwmon->count);
-	temp->temp_input.attr.attr.name = temp->temp_input.name;
+	temp->temp_input.attr.attr.name = "temp1_input";
 	temp->temp_input.attr.attr.mode = 0444;
 	temp->temp_input.attr.show = temp_input_show;
 	sysfs_attr_init(&temp->temp_input.attr.attr);
 	result = device_create_file(hwmon->device, &temp->temp_input.attr);
 	if (result)
-		goto free_temp_mem;
+		goto unregister_name;
 
 	if (thermal_zone_crit_temp_valid(tz)) {
-		snprintf(temp->temp_crit.name,
-				sizeof(temp->temp_crit.name),
-				"temp%d_crit", hwmon->count);
-		temp->temp_crit.attr.attr.name = temp->temp_crit.name;
+		temp->temp_crit.attr.attr.name = "temp1_crit";
 		temp->temp_crit.attr.attr.mode = 0444;
 		temp->temp_crit.attr.show = temp_crit_show;
 		sysfs_attr_init(&temp->temp_crit.attr.attr);
@@ -196,21 +145,17 @@ int thermal_add_hwmon_sysfs(struct therm
 		temp->temp_crit_present = true;
 	}
 
+	/* The list is needed for hwmon lookup during removal. */
 	mutex_lock(&thermal_hwmon_list_lock);
-	if (new_hwmon_device)
-		list_add_tail(&hwmon->node, &thermal_hwmon_list);
-	list_add_tail(&temp->hwmon_node, &hwmon->tz_list);
+	list_add_tail(&hwmon->node, &thermal_hwmon_list);
 	mutex_unlock(&thermal_hwmon_list_lock);
 
 	return 0;
 
  unregister_input:
 	device_remove_file(hwmon->device, &temp->temp_input.attr);
- free_temp_mem:
-	kfree(temp);
  unregister_name:
-	if (new_hwmon_device)
-		hwmon_device_unregister(hwmon->device);
+	hwmon_device_unregister(hwmon->device);
  free_mem:
 	kfree(hwmon);
 
@@ -218,39 +163,37 @@ int thermal_add_hwmon_sysfs(struct therm
 }
 EXPORT_SYMBOL_GPL(thermal_add_hwmon_sysfs);
 
+static struct thermal_hwmon_device *
+thermal_hwmon_lookup(const struct thermal_zone_device *tz)
+{
+	struct thermal_hwmon_device *hwmon;
+
+	list_for_each_entry(hwmon, &thermal_hwmon_list, node) {
+		if (hwmon->tz_temp.tz == tz)
+			return hwmon;
+	}
+	return NULL;
+}
+
 void thermal_remove_hwmon_sysfs(struct thermal_zone_device *tz)
 {
 	struct thermal_hwmon_device *hwmon;
 	struct thermal_hwmon_temp *temp;
 
-	hwmon = thermal_hwmon_lookup_by_type(tz);
-	if (unlikely(!hwmon)) {
-		/* Should never happen... */
-		dev_dbg(&tz->device, "hwmon device lookup failed!\n");
-		return;
-	}
+	scoped_guard(mutex, &thermal_hwmon_list_lock) {
+		hwmon = thermal_hwmon_lookup(tz);
+		if (!hwmon)
+			return;
 
-	temp = thermal_hwmon_lookup_temp(hwmon, tz);
-	if (unlikely(!temp)) {
-		/* Should never happen... */
-		dev_dbg(&tz->device, "temperature input lookup failed!\n");
-		return;
+		list_del(&hwmon->node);
 	}
 
+	temp = &hwmon->tz_temp;
+
 	device_remove_file(hwmon->device, &temp->temp_input.attr);
 	if (temp->temp_crit_present)
 		device_remove_file(hwmon->device, &temp->temp_crit.attr);
 
-	mutex_lock(&thermal_hwmon_list_lock);
-	list_del(&temp->hwmon_node);
-	kfree(temp);
-	if (!list_empty(&hwmon->tz_list)) {
-		mutex_unlock(&thermal_hwmon_list_lock);
-		return;
-	}
-	list_del(&hwmon->node);
-	mutex_unlock(&thermal_hwmon_list_lock);
-
 	hwmon_device_unregister(hwmon->device);
 	kfree(hwmon);
 }