> rtcdev = NULL
>
> CPU0 CPU 1
>
> alarmtimer_rtc_add_device(A)
> if (rtcdev) alarmtimer_rtc_add_device(B)
> return -EBUSY; if (rtcdev)
> mutex_lock(); return -EBUSY;
> rtcdev = A; mutex_lock();
> mutex_unlock;
>
> bla = alarmtimer_rtc_get_device()
>
> So bla = A
> mutex_lock() returns
> rtcdev = B;
> mutex_unlock();
>
> The next call to alarmtimer_rtc_get_device() will return B. Not what
> you want. Maybe you want that, but then your patch is missing an
> explanation why you want that and why this would be a desired
> behaviour.
>
Based on current implementation alarmtimer_rtc_add_device() will just
be called once thru class interface, also &parent->p->mutex is there to protect
the class_intf->add_dev() calling, so we can remove rtcdev_lock.
Is it making sense?
Subject: [PATCH] alarmtimer: Removing the usage of lock rtcdev_lock
alarmtimer_rtc_add_device() will be called once at the time
alarmtimer_init() is called.
alarmtimer_init -->
alarmtimer_rtc_interface_setup -->
class_interface_register -->
mutex_lock(&parent->p->mutex)
...
class_intf->add_dev()/alarmtimer_rtc_add_device
...
mutex_unlock(&parent->p->mutex);
But also the mutex parent->p->mutex has protected the add_dev()
callback.
So here removing the lock of rtcdev_lock.
Signed-off-by: liu chuansheng <chuansheng....@intel.com>
---
kernel/time/alarmtimer.c | 13 ++++---------
1 files changed, 4 insertions(+), 9 deletions(-)
diff --git a/kernel/time/alarmtimer.c b/kernel/time/alarmtimer.c
index eed3b26..660091c 100644
--- a/kernel/time/alarmtimer.c
+++ b/kernel/time/alarmtimer.c
@@ -51,7 +51,6 @@ static struct wakeup_source *ws;
/* rtc timer and device for setting alarm wakeups at suspend */
static struct rtc_timer rtctimer;
static struct rtc_device *rtcdev;
-static DEFINE_SPINLOCK(rtcdev_lock);
/**
* alarmtimer_get_rtcdev - Return selected rtcdevice
@@ -69,7 +68,6 @@ struct rtc_device *alarmtimer_get_rtcdev(void)
static int alarmtimer_rtc_add_device(struct device *dev,
struct class_interface *class_intf)
{
- unsigned long flags;
struct rtc_device *rtc = to_rtc_device(dev);
if (rtcdev)
@@ -80,13 +78,10 @@ static int alarmtimer_rtc_add_device(struct device *dev,
if (!device_may_wakeup(rtc->dev.parent))
return -1;
- spin_lock_irqsave(&rtcdev_lock, flags);
- if (!rtcdev) {
- rtcdev = rtc;
- /* hold a reference so it doesn't go away */
- get_device(dev);
- }
- spin_unlock_irqrestore(&rtcdev_lock, flags);
+ rtcdev = rtc;
+ /* hold a reference so it doesn't go away */
+ get_device(dev);
+
return 0;
}
--
1.7.0.4
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