Merge branch 'clockevents/fixes' of git://git.linaro.org/people/daniel.lezcano/linux...

[linux-drm-fsl-dcu.git] / include / linux / seqlock.h

diff --git a/include/linux/seqlock.h b/include/linux/seqlock.h
index 1e8a8b6e837d8621fa5488f832273df673ff3520..cf87a24c0f92f1963081c93d7b0cce2356025358 100644 (file)
--- a/include/linux/seqlock.h
+++ b/include/linux/seqlock.h
@@ -354,6 +354,35 @@ static inline void read_sequnlock_excl(seqlock_t *sl)
        spin_unlock(&sl->lock);
 }
 
+/**
+ * read_seqbegin_or_lock - begin a sequence number check or locking block
+ * @lock: sequence lock
+ * @seq : sequence number to be checked
+ *
+ * First try it once optimistically without taking the lock. If that fails,
+ * take the lock. The sequence number is also used as a marker for deciding
+ * whether to be a reader (even) or writer (odd).
+ * N.B. seq must be initialized to an even number to begin with.
+ */
+static inline void read_seqbegin_or_lock(seqlock_t *lock, int *seq)
+{
+       if (!(*seq & 1))        /* Even */
+               *seq = read_seqbegin(lock);
+       else                    /* Odd */
+               read_seqlock_excl(lock);
+}
+
+static inline int need_seqretry(seqlock_t *lock, int seq)
+{
+       return !(seq & 1) && read_seqretry(lock, seq);
+}
+
+static inline void done_seqretry(seqlock_t *lock, int seq)
+{
+       if (seq & 1)
+               read_sequnlock_excl(lock);
+}
+
 static inline void read_seqlock_excl_bh(seqlock_t *sl)
 {
        spin_lock_bh(&sl->lock);