From 5a0015d62668e64c8b6e02e360fbbea121bfd5e6 Mon Sep 17 00:00:00 2001 From: Chris Zankel Date: Thu, 23 Jun 2005 22:01:16 -0700 Subject: [PATCH] xtensa: Architecture support for Tensilica Xtensa Part 3 The attached patches provides part 3 of an architecture implementation for the Tensilica Xtensa CPU series. Signed-off-by: Chris Zankel Signed-off-by: Andrew Morton Signed-off-by: Linus Torvalds --- arch/xtensa/kernel/semaphore.c | 226 +++++++++++++++++++++++++++++++++++++++++ 1 file changed, 226 insertions(+) create mode 100644 arch/xtensa/kernel/semaphore.c (limited to 'arch/xtensa/kernel/semaphore.c') diff --git a/arch/xtensa/kernel/semaphore.c b/arch/xtensa/kernel/semaphore.c new file mode 100644 index 000000000000..d40f4b1b75ac --- /dev/null +++ b/arch/xtensa/kernel/semaphore.c @@ -0,0 +1,226 @@ +/* + * arch/xtensa/kernel/semaphore.c + * + * Generic semaphore code. Buyer beware. Do your own specific changes + * in + * + * This file is subject to the terms and conditions of the GNU General Public + * License. See the file "COPYING" in the main directory of this archive + * for more details. + * + * Copyright (C) 2001 - 2005 Tensilica Inc. + * + * Joe Taylor + * Chris Zankel + * Marc Gauthier + * Kevin Chea + */ + +#include +#include +#include +#include +#include + +/* + * These two _must_ execute atomically wrt each other. + */ + +static __inline__ void wake_one_more(struct semaphore * sem) +{ + atomic_inc((atomic_t *)&sem->sleepers); +} + +static __inline__ int waking_non_zero(struct semaphore *sem) +{ + unsigned long flags; + int ret = 0; + + spin_lock_irqsave(&semaphore_wake_lock, flags); + if (sem->sleepers > 0) { + sem->sleepers--; + ret = 1; + } + spin_unlock_irqrestore(&semaphore_wake_lock, flags); + return ret; +} + +/* + * waking_non_zero_interruptible: + * 1 got the lock + * 0 go to sleep + * -EINTR interrupted + * + * We must undo the sem->count down_interruptible() increment while we are + * protected by the spinlock in order to make atomic this atomic_inc() with the + * atomic_read() in wake_one_more(), otherwise we can race. -arca + */ + +static __inline__ int waking_non_zero_interruptible(struct semaphore *sem, + struct task_struct *tsk) +{ + unsigned long flags; + int ret = 0; + + spin_lock_irqsave(&semaphore_wake_lock, flags); + if (sem->sleepers > 0) { + sem->sleepers--; + ret = 1; + } else if (signal_pending(tsk)) { + atomic_inc(&sem->count); + ret = -EINTR; + } + spin_unlock_irqrestore(&semaphore_wake_lock, flags); + return ret; +} + +/* + * waking_non_zero_trylock: + * 1 failed to lock + * 0 got the lock + * + * We must undo the sem->count down_trylock() increment while we are + * protected by the spinlock in order to make atomic this atomic_inc() with the + * atomic_read() in wake_one_more(), otherwise we can race. -arca + */ + +static __inline__ int waking_non_zero_trylock(struct semaphore *sem) +{ + unsigned long flags; + int ret = 1; + + spin_lock_irqsave(&semaphore_wake_lock, flags); + if (sem->sleepers <= 0) + atomic_inc(&sem->count); + else { + sem->sleepers--; + ret = 0; + } + spin_unlock_irqrestore(&semaphore_wake_lock, flags); + return ret; +} + +spinlock_t semaphore_wake_lock; + +/* + * Semaphores are implemented using a two-way counter: + * The "count" variable is decremented for each process + * that tries to sleep, while the "waking" variable is + * incremented when the "up()" code goes to wake up waiting + * processes. + * + * Notably, the inline "up()" and "down()" functions can + * efficiently test if they need to do any extra work (up + * needs to do something only if count was negative before + * the increment operation. + * + * waking_non_zero() (from asm/semaphore.h) must execute + * atomically. + * + * When __up() is called, the count was negative before + * incrementing it, and we need to wake up somebody. + * + * This routine adds one to the count of processes that need to + * wake up and exit. ALL waiting processes actually wake up but + * only the one that gets to the "waking" field first will gate + * through and acquire the semaphore. The others will go back + * to sleep. + * + * Note that these functions are only called when there is + * contention on the lock, and as such all this is the + * "non-critical" part of the whole semaphore business. The + * critical part is the inline stuff in + * where we want to avoid any extra jumps and calls. + */ + +void __up(struct semaphore *sem) +{ + wake_one_more(sem); + wake_up(&sem->wait); +} + +/* + * Perform the "down" function. Return zero for semaphore acquired, + * return negative for signalled out of the function. + * + * If called from __down, the return is ignored and the wait loop is + * not interruptible. This means that a task waiting on a semaphore + * using "down()" cannot be killed until someone does an "up()" on + * the semaphore. + * + * If called from __down_interruptible, the return value gets checked + * upon return. If the return value is negative then the task continues + * with the negative value in the return register (it can be tested by + * the caller). + * + * Either form may be used in conjunction with "up()". + * + */ + +#define DOWN_VAR \ + struct task_struct *tsk = current; \ + wait_queue_t wait; \ + init_waitqueue_entry(&wait, tsk); + +#define DOWN_HEAD(task_state) \ + \ + \ + tsk->state = (task_state); \ + add_wait_queue(&sem->wait, &wait); \ + \ + /* \ + * Ok, we're set up. sem->count is known to be less than zero \ + * so we must wait. \ + * \ + * We can let go the lock for purposes of waiting. \ + * We re-acquire it after awaking so as to protect \ + * all semaphore operations. \ + * \ + * If "up()" is called before we call waking_non_zero() then \ + * we will catch it right away. If it is called later then \ + * we will have to go through a wakeup cycle to catch it. \ + * \ + * Multiple waiters contend for the semaphore lock to see \ + * who gets to gate through and who has to wait some more. \ + */ \ + for (;;) { + +#define DOWN_TAIL(task_state) \ + tsk->state = (task_state); \ + } \ + tsk->state = TASK_RUNNING; \ + remove_wait_queue(&sem->wait, &wait); + +void __sched __down(struct semaphore * sem) +{ + DOWN_VAR + DOWN_HEAD(TASK_UNINTERRUPTIBLE) + if (waking_non_zero(sem)) + break; + schedule(); + DOWN_TAIL(TASK_UNINTERRUPTIBLE) +} + +int __sched __down_interruptible(struct semaphore * sem) +{ + int ret = 0; + DOWN_VAR + DOWN_HEAD(TASK_INTERRUPTIBLE) + + ret = waking_non_zero_interruptible(sem, tsk); + if (ret) + { + if (ret == 1) + /* ret != 0 only if we get interrupted -arca */ + ret = 0; + break; + } + schedule(); + DOWN_TAIL(TASK_INTERRUPTIBLE) + return ret; +} + +int __down_trylock(struct semaphore * sem) +{ + return waking_non_zero_trylock(sem); +} -- cgit v1.2.3