[PATCH v5 1/4] PM: Add a sysfs file to represent time spent in hardware sleep state

[Mario Limonciello]

Userspace can't easily discover how much of a sleep cycle was spent in a
hardware sleep state without using kernel tracing and vendor specific sysfs
or debugfs files.

To make this information more discoverable, introduce a new sysfs file
to represent the time spent in a sleep state.
This file will be present only if the system supports s2idle.

Signed-off-by: Mario Limonciello <mario.limonciello@xxxxxxx>
---
v4->v5:
 * Provide time in microseconds instead of percent. Userspace can convert
   this if desirable.
---
 Documentation/ABI/testing/sysfs-power |  9 +++++++++
 include/linux/suspend.h               |  2 ++
 kernel/power/main.c                   | 29 +++++++++++++++++++++++++++
 3 files changed, 40 insertions(+)

diff --git a/Documentation/ABI/testing/sysfs-power b/Documentation/ABI/testing/sysfs-power
index f99d433ff311..9e0c31b9ce85 100644
--- a/Documentation/ABI/testing/sysfs-power
+++ b/Documentation/ABI/testing/sysfs-power
@@ -413,6 +413,15 @@ Description:
 		The /sys/power/suspend_stats/last_failed_step file contains
 		the last failed step in the suspend/resume path.
 
+What:		/sys/power/suspend_stats/last_hw_sleep
+Date:		June 2023
+Contact:	Mario Limonciello <mario.limonciello@xxxxxxx>
+Description:
+		The /sys/power/suspend_stats/last_hw_sleep file
+		contains the duration of time spent in a hardware sleep
+		state during from the previous suspend cycle. This number
+		is measured in microseconds.
+
 What:		/sys/power/sync_on_suspend
 Date:		October 2019
 Contact:	Jonas Meurer <jonas@xxxxxxxxxxxxxxx>
diff --git a/include/linux/suspend.h b/include/linux/suspend.h
index cfe19a028918..e0f2ac5f4406 100644
--- a/include/linux/suspend.h
+++ b/include/linux/suspend.h
@@ -68,6 +68,7 @@ struct suspend_stats {
 	int	last_failed_errno;
 	int	errno[REC_FAILED_NUM];
 	int	last_failed_step;
+	u64	last_hw_sleep;
 	enum suspend_stat_step	failed_steps[REC_FAILED_NUM];
 };
 
@@ -489,6 +490,7 @@ void restore_processor_state(void);
 extern int register_pm_notifier(struct notifier_block *nb);
 extern int unregister_pm_notifier(struct notifier_block *nb);
 extern void ksys_sync_helper(void);
+extern void pm_set_hw_sleep_time(u64 t);
 
 #define pm_notifier(fn, pri) {				\
 	static struct notifier_block fn##_nb =			\
diff --git a/kernel/power/main.c b/kernel/power/main.c
index 31ec4a9b9d70..6a2bf8784ce8 100644
--- a/kernel/power/main.c
+++ b/kernel/power/main.c
@@ -6,6 +6,7 @@
  * Copyright (c) 2003 Open Source Development Lab
  */
 
+#include <linux/acpi.h>
 #include <linux/export.h>
 #include <linux/kobject.h>
 #include <linux/string.h>
@@ -83,6 +84,12 @@ int unregister_pm_notifier(struct notifier_block *nb)
 }
 EXPORT_SYMBOL_GPL(unregister_pm_notifier);
 
+void pm_set_hw_sleep_time(u64 t)
+{
+	suspend_stats.last_hw_sleep = t;
+}
+EXPORT_SYMBOL_GPL(pm_set_hw_sleep_time);
+
 int pm_notifier_call_chain_robust(unsigned long val_up, unsigned long val_down)
 {
 	int ret;
@@ -377,6 +384,13 @@ static ssize_t last_failed_step_show(struct kobject *kobj,
 }
 static struct kobj_attribute last_failed_step = __ATTR_RO(last_failed_step);
 
+static ssize_t last_hw_sleep_show(struct kobject *kobj,
+		struct kobj_attribute *attr, char *buf)
+{
+	return sysfs_emit(buf, "%llu\n", suspend_stats.last_hw_sleep);
+}
+static struct kobj_attribute last_hw_sleep = __ATTR_RO(last_hw_sleep);
+
 static struct attribute *suspend_attrs[] = {
 	&success.attr,
 	&fail.attr,
@@ -391,12 +405,27 @@ static struct attribute *suspend_attrs[] = {
 	&last_failed_dev.attr,
 	&last_failed_errno.attr,
 	&last_failed_step.attr,
+	&last_hw_sleep.attr,
 	NULL,
 };
 
+static umode_t suspend_attr_is_visible(struct kobject *kobj, struct attribute *attr, int idx)
+{
+	if (attr == &last_hw_sleep.attr) {
+#ifdef CONFIG_ACPI
+		if (acpi_gbl_FADT.flags & ACPI_FADT_LOW_POWER_S0)
+			return 0444;
+#endif
+		return 0;
+	}
+
+	return 0444;
+}
+
 static const struct attribute_group suspend_attr_group = {
 	.name = "suspend_stats",
 	.attrs = suspend_attrs,
+	.is_visible = suspend_attr_is_visible,
 };
 
 #ifdef CONFIG_DEBUG_FS
-- 
2.34.1