1 files changed, 221 insertions, 0 deletions

diff --git a/arch/tile/lib/spinlock_32.c b/arch/tile/lib/spinlock_32.c
new file mode 100644
index 000000000000..485e24d62c6b
--- /dev/null
+++ b/arch/tile/lib/spinlock_32.c
@@ -0,0 +1,221 @@
+/*
+ * Copyright 2010 Tilera Corporation. All Rights Reserved.
+ *
+ *   This program is free software; you can redistribute it and/or
+ *   modify it under the terms of the GNU General Public License
+ *   as published by the Free Software Foundation, version 2.
+ *
+ *   This program is distributed in the hope that it will be useful, but
+ *   WITHOUT ANY WARRANTY; without even the implied warranty of
+ *   MERCHANTABILITY OR FITNESS FOR A PARTICULAR PURPOSE, GOOD TITLE or
+ *   NON INFRINGEMENT.  See the GNU General Public License for
+ *   more details.
+ */
+
+#include <linux/spinlock.h>
+#include <linux/module.h>
+#include <asm/processor.h>
+
+#include "spinlock_common.h"
+
+void arch_spin_lock(arch_spinlock_t *lock)
+{
+        int my_ticket;
+        int iterations = 0;
+        int delta;
+
+        while ((my_ticket = __insn_tns((void *)&lock->next_ticket)) & 1)
+                delay_backoff(iterations++);
+
+        /* Increment the next ticket number, implicitly releasing tns lock. */
+        lock->next_ticket = my_ticket + TICKET_QUANTUM;
+
+        /* Wait until it's our turn. */
+        while ((delta = my_ticket - lock->current_ticket) != 0)
+                relax((128 / CYCLES_PER_RELAX_LOOP) * delta);
+}
+EXPORT_SYMBOL(arch_spin_lock);
+
+int arch_spin_trylock(arch_spinlock_t *lock)
+{
+        /*
+         * Grab a ticket; no need to retry if it's busy, we'll just
+         * treat that the same as "locked", since someone else
+         * will lock it momentarily anyway.
+         */
+        int my_ticket = __insn_tns((void *)&lock->next_ticket);
+
+        if (my_ticket == lock->current_ticket) {
+                /* Not currently locked, so lock it by keeping this ticket. */
+                lock->next_ticket = my_ticket + TICKET_QUANTUM;
+                /* Success! */
+                return 1;
+        }
+
+        if (!(my_ticket & 1)) {
+                /* Release next_ticket. */
+                lock->next_ticket = my_ticket;
+        }
+
+        return 0;
+}
+EXPORT_SYMBOL(arch_spin_trylock);
+
+void arch_spin_unlock_wait(arch_spinlock_t *lock)
+{
+        u32 iterations = 0;
+        while (arch_spin_is_locked(lock))
+                delay_backoff(iterations++);
+}
+EXPORT_SYMBOL(arch_spin_unlock_wait);
+
+/*
+ * The low byte is always reserved to be the marker for a "tns" operation
+ * since the low bit is set to "1" by a tns.  The next seven bits are
+ * zeroes.  The next byte holds the "next" writer value, i.e. the ticket
+ * available for the next task that wants to write.  The third byte holds
+ * the current writer value, i.e. the writer who holds the current ticket.
+ * If current == next == 0, there are no interested writers.
+ */
+#define WR_NEXT_SHIFT   _WR_NEXT_SHIFT
+#define WR_CURR_SHIFT   _WR_CURR_SHIFT
+#define WR_WIDTH        _WR_WIDTH
+#define WR_MASK         ((1 << WR_WIDTH) - 1)
+
+/*
+ * The last eight bits hold the active reader count.  This has to be
+ * zero before a writer can start to write.
+ */
+#define RD_COUNT_SHIFT  _RD_COUNT_SHIFT
+#define RD_COUNT_WIDTH  _RD_COUNT_WIDTH
+#define RD_COUNT_MASK   ((1 << RD_COUNT_WIDTH) - 1)
+
+
+/* Lock the word, spinning until there are no tns-ers. */
+static inline u32 get_rwlock(arch_rwlock_t *rwlock)
+{
+        u32 iterations = 0;
+        for (;;) {
+                u32 val = __insn_tns((int *)&rwlock->lock);
+                if (unlikely(val & 1)) {
+                        delay_backoff(iterations++);
+                        continue;
+                }
+                return val;
+        }
+}
+
+int arch_read_trylock_slow(arch_rwlock_t *rwlock)
+{
+        u32 val = get_rwlock(rwlock);
+        int locked = (val << RD_COUNT_WIDTH) == 0;
+        rwlock->lock = val + (locked << RD_COUNT_SHIFT);
+        return locked;
+}
+EXPORT_SYMBOL(arch_read_trylock_slow);
+
+void arch_read_unlock_slow(arch_rwlock_t *rwlock)
+{
+        u32 val = get_rwlock(rwlock);
+        rwlock->lock = val - (1 << RD_COUNT_SHIFT);
+}
+EXPORT_SYMBOL(arch_read_unlock_slow);
+
+void arch_write_unlock_slow(arch_rwlock_t *rwlock, u32 val)
+{
+        u32 eq, mask = 1 << WR_CURR_SHIFT;
+        while (unlikely(val & 1)) {
+                /* Limited backoff since we are the highest-priority task. */
+                relax(4);
+                val = __insn_tns((int *)&rwlock->lock);
+        }
+        val = __insn_addb(val, mask);
+        eq = __insn_seqb(val, val << (WR_CURR_SHIFT - WR_NEXT_SHIFT));
+        val = __insn_mz(eq & mask, val);
+        rwlock->lock = val;
+}
+EXPORT_SYMBOL(arch_write_unlock_slow);
+
+/*
+ * We spin until everything but the reader bits (which are in the high
+ * part of the word) are zero, i.e. no active or waiting writers, no tns.
+ *
+ * ISSUE: This approach can permanently starve readers.  A reader who sees
+ * a writer could instead take a ticket lock (just like a writer would),
+ * and atomically enter read mode (with 1 reader) when it gets the ticket.
+ * This way both readers and writers will always make forward progress
+ * in a finite time.
+ */
+void arch_read_lock_slow(arch_rwlock_t *rwlock, u32 val)
+{
+        u32 iterations = 0;
+        do {
+                if (!(val & 1))
+                        rwlock->lock = val;
+                delay_backoff(iterations++);
+                val = __insn_tns((int *)&rwlock->lock);
+        } while ((val << RD_COUNT_WIDTH) != 0);
+        rwlock->lock = val + (1 << RD_COUNT_SHIFT);
+}
+EXPORT_SYMBOL(arch_read_lock_slow);
+
+void arch_write_lock_slow(arch_rwlock_t *rwlock, u32 val)
+{
+        /*
+         * The trailing underscore on this variable (and curr_ below)
+         * reminds us that the high bits are garbage; we mask them out
+         * when we compare them.
+         */
+        u32 my_ticket_;
+
+        /* Take out the next ticket; this will also stop would-be readers. */
+        if (val & 1)
+                val = get_rwlock(rwlock);
+        rwlock->lock = __insn_addb(val, 1 << WR_NEXT_SHIFT);
+
+        /* Extract my ticket value from the original word. */
+        my_ticket_ = val >> WR_NEXT_SHIFT;
+
+        /*
+         * Wait until the "current" field matches our ticket, and
+         * there are no remaining readers.
+         */
+        for (;;) {
+                u32 curr_ = val >> WR_CURR_SHIFT;
+                u32 readers = val >> RD_COUNT_SHIFT;
+                u32 delta = ((my_ticket_ - curr_) & WR_MASK) + !!readers;
+                if (likely(delta == 0))
+                        break;
+
+                /* Delay based on how many lock-holders are still out there. */
+                relax((256 / CYCLES_PER_RELAX_LOOP) * delta);
+
+                /*
+                 * Get a non-tns value to check; we don't need to tns
+                 * it ourselves.  Since we're not tns'ing, we retry
+                 * more rapidly to get a valid value.
+                 */
+                while ((val = rwlock->lock) & 1)
+                        relax(4);
+        }
+}
+EXPORT_SYMBOL(arch_write_lock_slow);
+
+int __tns_atomic_acquire(atomic_t *lock)
+{
+        int ret;
+        u32 iterations = 0;
+
+        BUG_ON(__insn_mfspr(SPR_INTERRUPT_CRITICAL_SECTION));
+        __insn_mtspr(SPR_INTERRUPT_CRITICAL_SECTION, 1);
+
+        while ((ret = __insn_tns((void *)&lock->counter)) == 1)
+                delay_backoff(iterations++);
+        return ret;
+}
+
+void __tns_atomic_release(atomic_t *p, int v)
+{
+        p->counter = v;
+        __insn_mtspr(SPR_INTERRUPT_CRITICAL_SECTION, 0);
+}