45  * In particular; where the traditional MCS lock consists of a tail pointer
47  * unlock the next pending (next->locked), we compress both these: {tail,
53  * we can encode the tail by combining the 2-bit nesting level with the cpu
54  * number. With one byte for the lock value and 3 bytes for the tail, only a
112  * We must be able to distinguish between no-tail and the tail at 0:0,
118 	u32 tail;  in encode_tail()  local
120 	tail  = (cpu + 1) << _Q_TAIL_CPU_OFFSET;  in encode_tail()
121 	tail |= idx << _Q_TAIL_IDX_OFFSET; /* assume < 4 */  in encode_tail()
123 	return tail;  in encode_tail()
126 static inline __pure struct mcs_spinlock *decode_tail(u32 tail)  in decode_tail()  argument
128 	int cpu = (tail >> _Q_TAIL_CPU_OFFSET) - 1;  in decode_tail()
129 	int idx = (tail &  _Q_TAIL_IDX_MASK) >> _Q_TAIL_IDX_OFFSET;  in decode_tail()
168  * xchg_tail - Put in the new queue tail code word & retrieve previous one
170  * @tail : The new queue tail code word
171  * Return: The previous queue tail code word
173  * xchg(lock, tail), which heads an address dependency
177 static __always_inline u32 xchg_tail(struct qspinlock *lock, u32 tail)  in xchg_tail()  argument
181 	 * MCS node is properly initialized before updating the tail.  in xchg_tail()
183 	return (u32)xchg_relaxed(&lock->tail,  in xchg_tail()
184 				 tail >> _Q_TAIL_OFFSET) << _Q_TAIL_OFFSET;  in xchg_tail()
212  * xchg_tail - Put in the new queue tail code word & retrieve previous one
214  * @tail : The new queue tail code word
215  * Return: The previous queue tail code word
217  * xchg(lock, tail)
221 static __always_inline u32 xchg_tail(struct qspinlock *lock, u32 tail)  in xchg_tail()  argument
226 		new = (val & _Q_LOCKED_PENDING_MASK) | tail;  in xchg_tail()
230 		 * tail.  in xchg_tail()
300  * (queue tail, pending bit, lock value)
319 	u32 old, tail;  in queued_spin_lock_slowpath()  local
403 	tail = encode_tail(smp_processor_id(), idx);  in queued_spin_lock_slowpath()
451 	 * publish the updated tail via xchg_tail() and potentially link  in queued_spin_lock_slowpath()
457 	 * Publish the updated tail.  in queued_spin_lock_slowpath()
463 	old = xchg_tail(lock, tail);  in queued_spin_lock_slowpath()
523 	 * If the queue head is the only one in the queue (lock value == tail)  in queued_spin_lock_slowpath()
524 	 * and nobody is pending, clear the tail code and grab the lock.  in queued_spin_lock_slowpath()
538 	if ((val & _Q_TAIL_MASK) == tail) {  in queued_spin_lock_slowpath()
545 	 * which will then detect the remaining tail and queue behind us  in queued_spin_lock_slowpath()