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

Pranav Prasad
2024-02-07T10:06:33Z

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@google.com>
Signed-off-by: Kelly Rossmoyer <krossmo@google.com>
---
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..e5d2e560b4c1 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 u64 suspend_check_duration_ns = 2 * NSEC_PER_SEC;
+
+static ssize_t suspend_check_duration_show(struct kobject *kobj,
+ struct kobj_attribute *attr, char *buf)
+{
+ return sysfs_emit(buf, "%llu\n", suspend_check_duration_ns);
+}
+
+static ssize_t suspend_check_duration_store(struct kobject *kobj,
+ struct kobj_attribute *attr, const char *buf, size_t n)
+{
+ u64 val;
+
+ if (kstrtou64(buf, 10, &val))
+ return -EINVAL;
+
+ suspend_check_duration_ns = 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_ns) {
+ pm_wakeup_event(dev, suspend_check_duration_ns/NSEC_PER_MSEC);
return -EBUSY;
}

--
2.43.0.594.gd9cf4e227d-goog