thermal: Introduce a debugfs-based testing facility

Introduce a facility allowing the thermal core functionality to be
exercised in a controlled way in order to verify its behavior, without
affecting its regular users noticeably.

It is based on the idea of preparing thermal zone templates along with
their trip points by writing to files in debugfs.  When ready, those
templates can be used for registering test thermal zones with the
thermal core.

The temperature of a test thermal zone created this way can be adjusted
via debugfs, which also triggers a __thermal_zone_device_update() call
for it.  By manipulating the temperature of a test thermal zone, one can
check if the thermal core reacts to the changes of it as expected.
Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com>
Link: https://patch.msgid.link/6065927.lOV4Wx5bFT@rjwysocki.net
[ rjw: Fixed ordering of kcalloc() arguments ]
[ rjw: Fixed debugfs_create_dir() return value checks ]
[ rjw: Fixed two kerneldoc comments ]
Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com>

drivers/thermal/Kconfig

@@ -40,6 +40,15 @@ config THERMAL_DEBUGFS
 	  Say Y to allow the thermal subsystem to collect diagnostic
 	  information that can be accessed via debugfs.
 
+config THERMAL_CORE_TESTING
+	tristate "Thermal core testing facility"
+	depends on DEBUG_FS
+	help
+	  Say Y to add a debugfs-based thermal core testing facility.
+	  It allows test thermal zones to be created and populated
+	  with trip points in order to exercise the thermal core
+	  functionality in a controlled way.
+
 config THERMAL_EMERGENCY_POWEROFF_DELAY_MS
 	int "Emergency poweroff delay in milli-seconds"
 	default 0

drivers/thermal/Makefile

@@ -63,3 +63,4 @@ obj-$(CONFIG_AMLOGIC_THERMAL)     += amlogic_thermal.o
 obj-$(CONFIG_SPRD_THERMAL)	+= sprd_thermal.o
 obj-$(CONFIG_KHADAS_MCU_FAN_THERMAL)	+= khadas_mcu_fan.o
 obj-$(CONFIG_LOONGSON2_THERMAL)	+= loongson2_thermal.o
+obj-$(CONFIG_THERMAL_CORE_TESTING)	+= testing/

drivers/thermal/testing/Makefile

+# SPDX-License-Identifier: GPL-2.0
+#
+# Thermal core testing facility.
+
+obj-$(CONFIG_THERMAL_CORE_TESTING) += thermal-testing.o
+
+thermal-testing-y := command.o zone.o

drivers/thermal/testing/command.c

+// SPDX-License-Identifier: GPL-2.0
+/*
+ * Copyright 2024, Intel Corporation
+ *
+ * Author: Rafael J. Wysocki <rafael.j.wysocki@intel.com>
+ *
+ * Thermal subsystem testing facility.
+ *
+ * This facility allows the thermal core functionality to be exercised in a
+ * controlled way in order to verify its behavior.
+ *
+ * It resides in the "thermal-testing" directory under the debugfs root and
+ * starts with a single file called "command" which can be written a string
+ * representing a thermal testing facility command.
+ *
+ * The currently supported commands are listed in the tt_commands enum below.
+ *
+ * The "addtz" command causes a new test thermal zone template to be created,
+ * for example:
+ *
+ * # echo addtz > /sys/kernel/debug/thermal-testing/command
+ *
+ * That template will be represented as a subdirectory in the "thermal-testing"
+ * directory, for example
+ *
+ * # ls /sys/kernel/debug/thermal-testing/
+ * command tz0
+ *
+ * The thermal zone template can be populated with trip points with the help of
+ * the "tzaddtrip" command, for example:
+ *
+ * # echo tzaddtrip:0 > /sys/kernel/debug/thermal-testing/command
+ *
+ * which causes a trip point template to be added to the test thermal zone
+ * template 0 (represented by the tz0 subdirectory in "thermal-testing").
+ *
+ * # ls /sys/kernel/debug/thermal-testing/tz0
+ * init_temp temp trip_0_temp trip_0_hyst
+ *
+ * The temperature of a trip point template is initially THERMAL_TEMP_INVALID
+ * and its hysteresis is initially 0.  They can be adjusted by writing to the
+ * "trip_x_temp" and "trip_x_hyst" files correspoinding to that trip point
+ * template, respectively.
+ *
+ * The initial temperature of a thermal zone based on a template can be set by
+ * writing to the "init_temp" file in its directory under "thermal-testing", for
+ * example:
+ *
+ * echo 50000 > /sys/kernel/debug/thermal-testing/tz0/init_temp
+ *
+ * When ready, "tzreg" command can be used for registering and enabling a
+ * thermal zone based on a given template with the thermal core, for example
+ *
+ * # echo tzreg:0 > /sys/kernel/debug/thermal-testing/command
+ *
+ * In this case, test thermal zone template 0 is used for registering a new
+ * thermal zone and the set of trip point templates associated with it is used
+ * for populating the new thermal zone's trip points table.  The type of the new
+ * thermal zone is "test_tz".
+ *
+ * The temperature and hysteresis of all of the trip points in that new thermal
+ * zone are adjustable via sysfs, so they can be updated at any time.
+ *
+ * The current temperature of the new thermal zone can be set by writing to the
+ * "temp" file in the corresponding thermal zone template's directory under
+ * "thermal-testing", for example
+ *
+ * echo 10000 > /sys/kernel/debug/thermal-testing/tz0/temp
+ *
+ * which will also trigger a temperature update for this zone in the thermal
+ * core, including checking its trip points, sending notifications to user space
+ * if any of them have been crossed and so on.
+ *
+ * When it is not needed any more, a test thermal zone template can be deleted
+ * with the help of the "deltz" command, for example
+ *
+ * # echo deltz:0 > /sys/kernel/debug/thermal-testing/command
+ *
+ * which will also unregister the thermal zone based on it, if present.
+ */
+
+#define pr_fmt(fmt) "thermal-testing: " fmt
+
+#include <linux/debugfs.h>
+#include <linux/module.h>
+
+#include "thermal_testing.h"
+
+struct dentry *d_testing;
+
+#define TT_COMMAND_SIZE		16
+
+enum tt_commands {
+	TT_CMD_ADDTZ,
+	TT_CMD_DELTZ,
+	TT_CMD_TZADDTRIP,
+	TT_CMD_TZREG,
+	TT_CMD_TZUNREG,
+};
+
+static const char *tt_command_strings[] = {
+	[TT_CMD_ADDTZ] = "addtz",
+	[TT_CMD_DELTZ] = "deltz",
+	[TT_CMD_TZADDTRIP] = "tzaddtrip",
+	[TT_CMD_TZREG] = "tzreg",
+	[TT_CMD_TZUNREG] = "tzunreg",
+};
+
+static int tt_command_exec(int index, const char *arg)
+{
+	int ret;
+
+	switch (index) {
+	case TT_CMD_ADDTZ:
+		ret = tt_add_tz();
+		break;
+
+	case TT_CMD_DELTZ:
+		ret = tt_del_tz(arg);
+		break;
+
+	case TT_CMD_TZADDTRIP:
+		ret = tt_zone_add_trip(arg);
+		break;
+
+	case TT_CMD_TZREG:
+		ret = tt_zone_reg(arg);
+		break;
+
+	case TT_CMD_TZUNREG:
+		ret = tt_zone_unreg(arg);
+		break;
+
+	default:
+		ret = -EINVAL;
+		break;
+	}
+
+	return ret;
+}
+
+static ssize_t tt_command_process(struct dentry *dentry, const char __user *user_buf,
+				  size_t count)
+{
+	char *buf __free(kfree);
+	char *arg;
+	int i;
+
+	buf = kmalloc(count + 1, GFP_KERNEL);
+	if (!buf)
+		return -ENOMEM;
+
+	if (copy_from_user(buf, user_buf, count))
+		return -EFAULT;
+
+	buf[count] = '\0';
+	strim(buf);
+
+	arg = strstr(buf, ":");
+	if (arg) {
+		*arg = '\0';
+		arg++;
+	}
+
+	for (i = 0; i < ARRAY_SIZE(tt_command_strings); i++) {
+		if (!strcmp(buf, tt_command_strings[i]))
+			return tt_command_exec(i, arg);
+	}
+
+	return -EINVAL;
+}
+
+static ssize_t tt_command_write(struct file *file, const char __user *user_buf,
+				size_t count, loff_t *ppos)
+{
+	struct dentry *dentry = file->f_path.dentry;
+	ssize_t ret;
+
+	if (*ppos)
+		return -EINVAL;
+
+	if (count + 1 > TT_COMMAND_SIZE)
+		return -E2BIG;
+
+	ret = debugfs_file_get(dentry);
+	if (unlikely(ret))
+		return ret;
+
+	ret = tt_command_process(dentry, user_buf, count);
+	if (ret)
+		return ret;
+
+	return count;
+}
+
+static const struct file_operations tt_command_fops = {
+	.write = tt_command_write,
+	.open =	 simple_open,
+	.llseek = default_llseek,
+};
+
+static int __init thermal_testing_init(void)
+{
+	d_testing = debugfs_create_dir("thermal-testing", NULL);
+	if (!IS_ERR(d_testing))
+		debugfs_create_file("command", 0200, d_testing, NULL,
+				    &tt_command_fops);
+
+	return 0;
+}
+module_init(thermal_testing_init);
+
+static void __exit thermal_testing_exit(void)
+{
+	debugfs_remove(d_testing);
+	tt_zone_cleanup();
+}
+module_exit(thermal_testing_exit);
+
+MODULE_DESCRIPTION("Thermal core testing facility");
+MODULE_LICENSE("GPL v2");

drivers/thermal/testing/thermal_testing.h

+/* SPDX-License-Identifier: GPL-2.0 */
+
+extern struct dentry *d_testing;
+
+int tt_add_tz(void);
+int tt_del_tz(const char *arg);
+int tt_zone_add_trip(const char *arg);
+int tt_zone_reg(const char *arg);
+int tt_zone_unreg(const char *arg);
+
+void tt_zone_cleanup(void);