Initial import

1 files changed, 259 insertions, 0 deletions

diff --git a/arch/tile/lib/spinlock_32.c b/arch/tile/lib/spinlock_32.c
new file mode 100644
index 000000000..b34f79aad
--- /dev/null
+++ b/arch/tile/lib/spinlock_32.c
@@ -0,0 +1,259 @@
+/*
+ * 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 <arch/spr_def.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)
+
+
+/*
+ * We can get the read lock if everything but the reader bits (which
+ * are in the high part of the word) is zero, i.e. no active or
+ * waiting writers, no tns.
+ *
+ * We guard the tns/store-back with an interrupt critical section to
+ * preserve the semantic that the same read lock can be acquired in an
+ * interrupt context.
+ */
+int arch_read_trylock(arch_rwlock_t *rwlock)
+{
+	u32 val;
+	__insn_mtspr(SPR_INTERRUPT_CRITICAL_SECTION, 1);
+	val = __insn_tns((int *)&rwlock->lock);
+	if (likely((val << _RD_COUNT_WIDTH) == 0)) {
+		val += 1 << RD_COUNT_SHIFT;
+		rwlock->lock = val;
+		__insn_mtspr(SPR_INTERRUPT_CRITICAL_SECTION, 0);
+		BUG_ON(val == 0);  /* we don't expect wraparound */
+		return 1;
+	}
+	if ((val & 1) == 0)
+		rwlock->lock = val;
+	__insn_mtspr(SPR_INTERRUPT_CRITICAL_SECTION, 0);
+	return 0;
+}
+EXPORT_SYMBOL(arch_read_trylock);
+
+/*
+ * Spin doing arch_read_trylock() until we acquire the lock.
+ * 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 would always make forward progress
+ * in a finite time.
+ */
+void arch_read_lock(arch_rwlock_t *rwlock)
+{
+	u32 iterations = 0;
+	while (unlikely(!arch_read_trylock(rwlock)))
+		delay_backoff(iterations++);
+}
+EXPORT_SYMBOL(arch_read_lock);
+
+void arch_read_unlock(arch_rwlock_t *rwlock)
+{
+	u32 val, iterations = 0;
+
+	mb();  /* guarantee anything modified under the lock is visible */
+	for (;;) {
+		__insn_mtspr(SPR_INTERRUPT_CRITICAL_SECTION, 1);
+		val = __insn_tns((int *)&rwlock->lock);
+		if (likely((val & 1) == 0)) {
+			rwlock->lock = val - (1 << _RD_COUNT_SHIFT);
+			__insn_mtspr(SPR_INTERRUPT_CRITICAL_SECTION, 0);
+			break;
+		}
+		__insn_mtspr(SPR_INTERRUPT_CRITICAL_SECTION, 0);
+		delay_backoff(iterations++);
+	}
+}
+EXPORT_SYMBOL(arch_read_unlock);
+
+/*
+ * We don't need an interrupt critical section here (unlike for
+ * arch_read_lock) since we should never use a bare write lock where
+ * it could be interrupted by code that could try to re-acquire it.
+ */
+void arch_write_lock(arch_rwlock_t *rwlock)
+{
+	/*
+	 * 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_;
+	u32 iterations = 0;
+	u32 val = __insn_tns((int *)&rwlock->lock);
+
+	if (likely(val == 0)) {
+		rwlock->lock = 1 << _WR_NEXT_SHIFT;
+		return;
+	}
+
+	/*
+	 * Wait until there are no readers, then bump up the next
+	 * field and capture the ticket value.
+	 */
+	for (;;) {
+		if (!(val & 1)) {
+			if ((val >> RD_COUNT_SHIFT) == 0)
+				break;
+			rwlock->lock = val;
+		}
+		delay_backoff(iterations++);
+		val = __insn_tns((int *)&rwlock->lock);
+	}
+
+	/* Take out the next ticket and extract my ticket value. */
+	rwlock->lock = __insn_addb(val, 1 << WR_NEXT_SHIFT);
+	my_ticket_ = val >> WR_NEXT_SHIFT;
+
+	/* Wait until the "current" field matches our ticket. */
+	for (;;) {
+		u32 curr_ = val >> WR_CURR_SHIFT;
+		u32 delta = ((my_ticket_ - curr_) & WR_MASK);
+		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);
+
+int arch_write_trylock(arch_rwlock_t *rwlock)
+{
+	u32 val = __insn_tns((int *)&rwlock->lock);
+
+	/*
+	 * If a tns is in progress, or there's a waiting or active locker,
+	 * or active readers, we can't take the lock, so give up.
+	 */
+	if (unlikely(val != 0)) {
+		if (!(val & 1))
+			rwlock->lock = val;
+		return 0;
+	}
+
+	/* Set the "next" field to mark it locked. */
+	rwlock->lock = 1 << _WR_NEXT_SHIFT;
+	return 1;
+}
+EXPORT_SYMBOL(arch_write_trylock);
+
+void arch_write_unlock(arch_rwlock_t *rwlock)
+{
+	u32 val, eq, mask;
+
+	mb();  /* guarantee anything modified under the lock is visible */
+	val = __insn_tns((int *)&rwlock->lock);
+	if (likely(val == (1 << _WR_NEXT_SHIFT))) {
+		rwlock->lock = 0;
+		return;
+	}
+	while (unlikely(val & 1)) {
+		/* Limited backoff since we are the highest-priority task. */
+		relax(4);
+		val = __insn_tns((int *)&rwlock->lock);
+	}
+	mask = 1 << WR_CURR_SHIFT;
+	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);