[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 <chris@zankel.net>
Signed-off-by: Andrew Morton <akpm@osdl.org>
Signed-off-by: Linus Torvalds <torvalds@osdl.org>

1 files changed, 226 insertions, 0 deletions

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 <asm/semaphore-helper.h>
+ *
+ * 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   <joe@tensilica.com, joetylr@yahoo.com>
+ * Chris Zankel <chris@zankel.net>
+ * Marc Gauthier<marc@tensilica.com, marc@alumni.uwaterloo.ca>
+ * Kevin Chea
+ */
+
+#include <linux/sched.h>
+#include <linux/wait.h>
+#include <linux/init.h>
+#include <asm/semaphore.h>
+#include <asm/errno.h>
+
+/*
+ * 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 <asm/semaphore.h>
+ * 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);
+}