[PATCH v2 1/2] alarmtimer: Create alarmtimer sysfs to make duration of kernel suspend check configurable

[Pranav Prasad]

Currently, the alarmtimer_suspend does not allow the kernel
to suspend if the next alarm is within 2 seconds.
Create alarmtimer sysfs to make the value of 2 seconds configurable.
This allows flexibility to provide a different value based on the
type of device running the Linux kernel. As a data point, about 40% of
kernel suspend failures in a subset of Android devices were due to
this check. A differently configured value can avoid these suspend
failures which performs a lot of additional work affecting the
power consumption of these Android devices.

Signed-off-by: Pranav Prasad <pranavpp@xxxxxxxxxx>
---
 kernel/time/alarmtimer.c | 61 ++++++++++++++++++++++++++++++++++++++--
 1 file changed, 58 insertions(+), 3 deletions(-)

diff --git a/kernel/time/alarmtimer.c b/kernel/time/alarmtimer.c
index 4657cb8e8b1f..e4b88c8dc0e1 100644
--- a/kernel/time/alarmtimer.c
+++ b/kernel/time/alarmtimer.c
@@ -33,6 +33,8 @@
 #define CREATE_TRACE_POINTS
 #include <trace/events/alarmtimer.h>
 
+static const char alarmtimer_group_name[] = "alarmtimer";
+
 /**
  * struct alarm_base - Alarm timer bases
  * @lock:		Lock for syncrhonized access to the base
@@ -63,6 +65,56 @@ static struct rtc_timer		rtctimer;
 static struct rtc_device	*rtcdev;
 static DEFINE_SPINLOCK(rtcdev_lock);
 
+/* Duration to check for soonest alarm during kernel suspend */
+static unsigned long suspend_check_duration_ms = 2 * MSEC_PER_SEC;
+
+static ssize_t suspend_check_duration_show(struct kobject *kobj,
+			struct kobj_attribute *attr, char *buf)
+{
+	return sysfs_emit(buf, "%lu\n", suspend_check_duration_ms);
+}
+
+static ssize_t suspend_check_duration_store(struct kobject *kobj,
+			struct kobj_attribute *attr, const char *buf, size_t n)
+{
+	unsigned long val;
+
+	if (kstrtoul(buf, 10, &val))
+		return -EINVAL;
+
+	suspend_check_duration_ms = val;
+
+	return n;
+}
+
+static struct kobj_attribute suspend_check_duration =
+			__ATTR_RW(suspend_check_duration);
+
+static struct attribute *alarmtimer_attrs[] = {
+	&suspend_check_duration.attr,
+	NULL,
+};
+
+static const struct attribute_group alarmtimer_attr_group = {
+	.name	= alarmtimer_group_name,
+	.attrs	= alarmtimer_attrs,
+};
+
+/**
+ * alarmtimer_sysfs_add - Adds sysfs attributes for alarmtimer
+ *
+ * Returns 0 if successful, non-zero value for error.
+ */
+static int alarmtimer_sysfs_add(void)
+{
+	int ret = sysfs_create_group(kernel_kobj, &alarmtimer_attr_group);
+
+	if (ret)
+		pr_warn("[%s] failed to create a sysfs group\n", __func__);
+
+	return ret;
+}
+
 /**
  * alarmtimer_get_rtcdev - Return selected rtcdevice
  *
@@ -98,8 +150,11 @@ static int alarmtimer_rtc_add_device(struct device *dev)
 
 	pdev = platform_device_register_data(dev, "alarmtimer",
 					     PLATFORM_DEVID_AUTO, NULL, 0);
-	if (!IS_ERR(pdev))
+	if (!IS_ERR(pdev)) {
 		device_init_wakeup(&pdev->dev, true);
+		if (alarmtimer_sysfs_add())
+			pr_warn("[%s] Failed to add alarmtimer sysfs attributes\n", __func__);
+	}
 
 	spin_lock_irqsave(&rtcdev_lock, flags);
 	if (!IS_ERR(pdev) && !rtcdev) {
@@ -279,8 +334,8 @@ static int alarmtimer_suspend(struct device *dev)
 	if (min == 0)
 		return 0;
 
-	if (ktime_to_ns(min) < 2 * NSEC_PER_SEC) {
-		pm_wakeup_event(dev, 2 * MSEC_PER_SEC);
+	if (ktime_to_ns(min) < suspend_check_duration_ms * NSEC_PER_MSEC) {
+		pm_wakeup_event(dev, suspend_check_duration_ms);
 		return -EBUSY;
 	}
 
-- 
2.43.0.687.g38aa6559b0-goog