[1/1,RFC] wakeup_reason: Add infrastructure to log and report why the system resumed from suspend.

diff --git a/Documentation/ABI/testing/sysfs-power b/Documentation/ABI/testing/sysfs-power
index 90ec4987074b..e79d7a49a24e 100644
--- a/Documentation/ABI/testing/sysfs-power
+++ b/Documentation/ABI/testing/sysfs-power
@@ -182,6 +182,15 @@  Description:
 		to a sleep state if any wakeup events are reported after the
 		write has returned.
 
+What:		/sys/power/last_wakeup_reason
+Date:		Jan 2022
+Contact:	Zichar Zhang <zichar.zhang@linaro.org>
+Description:
+		The /sys/power/last_wakeup_reason file shows the last reason
+		causing system "wake up" from suspend state. It could be an
+		interrupt signal, a kernel "wakeup_source" or just some other
+		reason logged into this file, and shows as a string.
+
 What:		/sys/power/reserved_size
 Date:		May 2011
 Contact:	Rafael J. Wysocki <rjw@rjwysocki.net>
diff --git a/drivers/base/power/wakeup.c b/drivers/base/power/wakeup.c
index 99bda0da23a8..a91ee1b8c0df 100644
--- a/drivers/base/power/wakeup.c
+++ b/drivers/base/power/wakeup.c
@@ -15,6 +15,7 @@ 
 #include <linux/seq_file.h>
 #include <linux/debugfs.h>
 #include <linux/pm_wakeirq.h>
+#include <linux/wakeup_reason.h>
 #include <trace/events/power.h>
 
 #include "power.h"
@@ -924,6 +925,7 @@  bool pm_wakeup_pending(void)
 
 	if (ret) {
 		pm_pr_dbg("Wakeup pending, aborting suspend\n");
+		log_ws_wakeup_reason();
 		pm_print_active_wakeup_sources();
 	}
 
@@ -947,11 +949,15 @@  void pm_wakeup_clear(bool reset)
 	pm_wakeup_irq = 0;
 	if (reset)
 		atomic_set(&pm_abort_suspend, 0);
+
+	clear_wakeup_reason();
 }
 
 void pm_system_irq_wakeup(unsigned int irq_number)
 {
 	if (pm_wakeup_irq == 0) {
+		log_irq_wakeup_reason(irq_number);
+
 		pm_wakeup_irq = irq_number;
 		pm_system_wakeup();
 	}
diff --git a/include/linux/wakeup_reason.h b/include/linux/wakeup_reason.h
new file mode 100644
index 000000000000..8d6e7a0e0bad
--- /dev/null
+++ b/include/linux/wakeup_reason.h
@@ -0,0 +1,35 @@ 
+/*
+ * include/linux/wakeup_reason.h
+ *
+ * Logs the reason which caused the kernel to resume
+ * from the suspend mode.
+ *
+ * Copyright (C) 2021 Linaro, Inc.
+ * This software is licensed under the terms of the GNU General Public
+ * License version 2, as published by the Free Software Foundation, and
+ * may be copied, distributed, and modified under those terms.
+ *
+ * This program is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+ * GNU General Public License for more details.
+ */
+
+#ifndef _LINUX_WAKEUP_REASON_H
+#define _LINUX_WAKEUP_REASON_H
+
+#define MAX_WAKEUP_REASON_STR_LEN 256
+
+#ifdef CONFIG_SUSPEND
+ssize_t log_ws_wakeup_reason(void);
+ssize_t log_irq_wakeup_reason(unsigned int irq_number);
+void clear_wakeup_reason(void);
+ssize_t last_wakeup_reason_get(char *buf, ssize_t max);
+#else
+ssize_t log_ws_wakeup_reason(void) { }
+ssize_t log_irq_wakeup_reason(unsigned int irq_number) { }
+void clear_wakeup_reason(void) { }
+ssize_t last_wakeup_reason_get(char *buf, ssize_t max) { }
+#endif
+
+#endif /* _LINUX_WAKEUP_REASON_H */
diff --git a/kernel/power/Makefile b/kernel/power/Makefile
index 5899260a8bef..73d77edc6a08 100644
--- a/kernel/power/Makefile
+++ b/kernel/power/Makefile
@@ -14,6 +14,7 @@  obj-$(CONFIG_HIBERNATION)	+= hibernate.o snapshot.o swap.o
 obj-$(CONFIG_HIBERNATION_SNAPSHOT_DEV) += user.o
 obj-$(CONFIG_PM_AUTOSLEEP)	+= autosleep.o
 obj-$(CONFIG_PM_WAKELOCKS)	+= wakelock.o
+obj-$(CONFIG_PM_SLEEP)		+= wakeup_reason.o
 
 obj-$(CONFIG_MAGIC_SYSRQ)	+= poweroff.o
 
diff --git a/kernel/power/main.c b/kernel/power/main.c
index 44169f3081fd..859af097813c 100644
--- a/kernel/power/main.c
+++ b/kernel/power/main.c
@@ -16,6 +16,7 @@ 
 #include <linux/suspend.h>
 #include <linux/syscalls.h>
 #include <linux/pm_runtime.h>
+#include <linux/wakeup_reason.h>
 
 #include "power.h"
 
@@ -739,6 +740,15 @@  static ssize_t wakeup_count_store(struct kobject *kobj,
 
 power_attr(wakeup_count);
 
+static ssize_t last_wakeup_reason_show(struct kobject *kobj,
+				struct kobj_attribute *attr,
+				char *buf)
+{
+	return last_wakeup_reason_get(buf, PAGE_SIZE);
+}
+
+power_attr_ro(last_wakeup_reason);
+
 #ifdef CONFIG_PM_AUTOSLEEP
 static ssize_t autosleep_show(struct kobject *kobj,
 			      struct kobj_attribute *attr,
@@ -892,6 +902,7 @@  static struct attribute * g[] = {
 #ifdef CONFIG_PM_SLEEP
 	&pm_async_attr.attr,
 	&wakeup_count_attr.attr,
+	&last_wakeup_reason_attr.attr,
 #ifdef CONFIG_SUSPEND
 	&mem_sleep_attr.attr,
 	&sync_on_suspend_attr.attr,
diff --git a/kernel/power/wakeup_reason.c b/kernel/power/wakeup_reason.c
new file mode 100644
index 000000000000..38d5f5e4d373
--- /dev/null
+++ b/kernel/power/wakeup_reason.c
@@ -0,0 +1,183 @@ 
+/*
+ * driver/base/power/wakeup_reason.c
+ *
+ * Logs the reasons which caused the kernel to resume from
+ * the suspend mode.
+ *
+ * Copyright (C) 2021 Linaro, Inc.
+ * This software is licensed under the terms of the GNU General Public
+ * License version 2, as published by the Free Software Foundation, and
+ * may be copied, distributed, and modified under those terms.
+ *
+ * This program is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+ * GNU General Public License for more details.
+ */
+
+#include <linux/kernel.h>
+#include <linux/irq.h>
+#include <linux/interrupt.h>
+#include <linux/io.h>
+#include <linux/init.h>
+#include <linux/spinlock.h>
+#include <linux/notifier.h>
+#include <linux/suspend.h>
+#include <linux/wakeup_reason.h>
+
+static DEFINE_SPINLOCK(wakeup_reason_lock);
+
+static bool capture_reasons;
+static char wakeup_reason_str[MAX_WAKEUP_REASON_STR_LEN];
+
+ssize_t log_ws_wakeup_reason(void)
+{
+	struct wakeup_source *ws, *last_active_ws = NULL;
+	int idx, max, len = 0;
+	bool active = false;
+	unsigned long flags;
+
+	spin_lock_irqsave(&wakeup_reason_lock, flags);
+
+	if (!capture_reasons) {
+		goto out;
+	}
+
+	idx = wakeup_sources_read_lock();
+	max = MAX_WAKEUP_REASON_STR_LEN;
+	for_each_wakeup_source(ws) {
+		if (ws->active && len < max) {
+			if (!active)
+				len += scnprintf(wakeup_reason_str, max,
+						"Pending Wakeup Sources: ");
+			len += scnprintf(wakeup_reason_str + len, max - len,
+				"%s ", ws->name);
+			active = true;
+		} else if (!active &&
+			   (!last_active_ws ||
+			    ktime_to_ns(ws->last_time) >
+			    ktime_to_ns(last_active_ws->last_time))) {
+			last_active_ws = ws;
+		}
+	}
+	if (!active && last_active_ws) {
+		len = scnprintf(wakeup_reason_str, max,
+				"Last active Wakeup Source: %s",
+				last_active_ws->name);
+	}
+	len += scnprintf(wakeup_reason_str + len, max - len, "\n");
+	wakeup_sources_read_unlock(idx);
+
+out:
+	spin_unlock_irqrestore(&wakeup_reason_lock, flags);
+
+	return len;
+}
+EXPORT_SYMBOL(log_ws_wakeup_reason);
+
+ssize_t log_irq_wakeup_reason(unsigned int irq_number)
+{
+	int len = 0;
+	struct irq_desc *desc;
+	const char *name = "null";
+	unsigned long flags;
+
+	desc = irq_to_desc(irq_number);
+	if (desc == NULL)
+		name = "stray irq";
+	else if (desc->action && desc->action->name)
+		name = desc->action->name;
+
+	spin_lock_irqsave(&wakeup_reason_lock, flags);
+
+	len = strnlen(wakeup_reason_str, MAX_WAKEUP_REASON_STR_LEN);
+	len += scnprintf(wakeup_reason_str + len,
+			MAX_WAKEUP_REASON_STR_LEN - len,
+			"%d %s\n", irq_number, name);
+
+	spin_unlock_irqrestore(&wakeup_reason_lock, flags);
+
+	return len;
+}
+EXPORT_SYMBOL(log_irq_wakeup_reason);
+
+void clear_wakeup_reason(void)
+{
+	unsigned long flags;
+
+	spin_lock_irqsave(&wakeup_reason_lock, flags);
+
+	memset(wakeup_reason_str, 0, sizeof(wakeup_reason_str));
+
+	spin_unlock_irqrestore(&wakeup_reason_lock, flags);
+}
+EXPORT_SYMBOL(clear_wakeup_reason);
+
+ssize_t last_wakeup_reason_get(char *buf, ssize_t max)
+{
+	ssize_t len, size = 0;
+	unsigned long flags;
+
+	if (!buf) {
+		return 0;
+	}
+
+	spin_lock_irqsave(&wakeup_reason_lock, flags);
+
+	len = strnlen(wakeup_reason_str, MAX_WAKEUP_REASON_STR_LEN);
+	if (len > 0) {
+		size = scnprintf(buf, max, "%s", wakeup_reason_str);
+	} else {
+		size = -ENODATA;
+	}
+
+	spin_unlock_irqrestore(&wakeup_reason_lock, flags);
+
+	return size;
+}
+EXPORT_SYMBOL(last_wakeup_reason_get);
+
+static int wakeup_reason_pm_event(struct notifier_block *notifier,
+		unsigned long pm_event, void *unused)
+{
+	unsigned long flags;
+
+	switch (pm_event) {
+	case PM_SUSPEND_PREPARE:
+		spin_lock_irqsave(&wakeup_reason_lock, flags);
+		capture_reasons = true;
+		spin_unlock_irqrestore(&wakeup_reason_lock, flags);
+
+		clear_wakeup_reason();
+		break;
+	case PM_POST_SUSPEND:
+		spin_lock_irqsave(&wakeup_reason_lock, flags);
+		capture_reasons = false;
+		if (!strnlen(wakeup_reason_str, MAX_WAKEUP_REASON_STR_LEN)) {
+			scnprintf(wakeup_reason_str, MAX_WAKEUP_REASON_STR_LEN,
+				"unknown wakeup reason, please check the kernel log\n");
+		}
+		spin_unlock_irqrestore(&wakeup_reason_lock, flags);
+
+		pr_debug("Resume caused by %s\n", wakeup_reason_str);
+		break;
+	default:
+		break;
+	}
+	return NOTIFY_DONE;
+}
+
+static struct notifier_block wakeup_reason_pm_notifier_block = {
+	.notifier_call = wakeup_reason_pm_event,
+};
+
+static int __init wakeup_reason_init(void)
+{
+	if (register_pm_notifier(&wakeup_reason_pm_notifier_block)) {
+		pr_warn("[%s] failed to register PM notifier\n", __func__);
+		return -EPERM;
+	}
+
+	return 0;
+}
+late_initcall(wakeup_reason_init);