timer: Added usleep[_range] timer

usleep[_range] are finer precision implementations of msleep
and are designed to be drop-in replacements for udelay where
a precise sleep / busy-wait is unnecessary. They also allow
an easy interface to specify slack when a precise (ish)
wakeup is unnecessary to help minimize wakeups

Signed-off-by: Patrick Pannuto <[e-mail]>
Cc: [e-mail]
Cc: [e-mail]
Acked-by: Arjan van de Ven <[e-mail]>
LKML-Reference: <[e-mail]>
Signed-off-by: Thomas Gleixner <[e-mail]>

include/linux/delay.h

···
 void calibrate_delay(void);
 void msleep(unsigned int msecs);
 unsigned long msleep_interruptible(unsigned int msecs);
+void usleep_range(unsigned long min, unsigned long max);
+
+static inline void usleep(unsigned long usecs)
+{
+	usleep_range(usecs, usecs);
+}
 
 static inline void ssleep(unsigned int seconds)
 {

kernel/timer.c

···
 }
 
 EXPORT_SYMBOL(msleep_interruptible);
+
+static int __sched do_usleep_range(unsigned long min, unsigned long max)
+{
+	ktime_t kmin;
+	unsigned long delta;
+
+	kmin = ktime_set(0, min * NSEC_PER_USEC);
+	delta = max - min;
+	return schedule_hrtimeout_range(&kmin, delta, HRTIMER_MODE_REL);
+}
+
+/**
+ * usleep_range - Drop in replacement for udelay where wakeup is flexible
+ * @min: Minimum time in usecs to sleep
+ * @max: Maximum time in usecs to sleep
+ */
+void usleep_range(unsigned long min, unsigned long max)
+{
+	__set_current_state(TASK_UNINTERRUPTIBLE);
+	do_usleep_range(min, max);
+}
+EXPORT_SYMBOL(usleep_range);