arm64: SMP support

This patch adds SMP initialisation and spinlocks implementation for
AArch64. The spinlock support uses the new load-acquire/store-release
instructions to avoid explicit barriers. The architecture also specifies
that an event is automatically generated when clearing the exclusive
monitor state to wake up processors in WFE, so there is no need for an
explicit DSB/SEV instruction sequence. The SEVL instruction is used to
set the exclusive monitor locally as there is no conditional WFE and a
branch is more expensive.

For the SMP booting protocol, see Documentation/arm64/booting.txt.

Signed-off-by: Will Deacon <will.deacon@arm.com>
Signed-off-by: Marc Zyngier <marc.zyngier@arm.com>
Signed-off-by: Catalin Marinas <catalin.marinas@arm.com>
Acked-by: Arnd Bergmann <arnd@arndb.de>
Acked-by: Tony Lindgren <tony@atomide.com>
Acked-by: Nicolas Pitre <nico@linaro.org>
Acked-by: Olof Johansson <olof@lixom.net>
Acked-by: Santosh Shilimkar <santosh.shilimkar@ti.com>
Acked-by: Arnd Bergmann <arnd@arndb.de>

1 files changed, 202 insertions, 0 deletions

diff --git a/arch/arm64/include/asm/spinlock.h b/arch/arm64/include/asm/spinlock.h
new file mode 100644
index 000000000000..41112fe2f8b1
--- /dev/null
+++ b/arch/arm64/include/asm/spinlock.h
@@ -0,0 +1,202 @@
+/*
+ * Copyright (C) 2012 ARM Ltd.
+ *
+ * This program is free software; you can redistribute it and/or modify
+ * it under the terms of the GNU General Public License version 2 as
+ * published by the Free Software Foundation.
+ *
+ * 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.  See the
+ * GNU General Public License for more details.
+ *
+ * You should have received a copy of the GNU General Public License
+ * along with this program.  If not, see <http://www.gnu.org/licenses/>.
+ */
+#ifndef __ASM_SPINLOCK_H
+#define __ASM_SPINLOCK_H
+
+#include <asm/spinlock_types.h>
+#include <asm/processor.h>
+
+/*
+ * Spinlock implementation.
+ *
+ * The old value is read exclusively and the new one, if unlocked, is written
+ * exclusively. In case of failure, the loop is restarted.
+ *
+ * The memory barriers are implicit with the load-acquire and store-release
+ * instructions.
+ *
+ * Unlocked value: 0
+ * Locked value: 1
+ */
+
+#define arch_spin_is_locked(x)          ((x)->lock != 0)
+#define arch_spin_unlock_wait(lock) \
+        do { while (arch_spin_is_locked(lock)) cpu_relax(); } while (0)
+
+#define arch_spin_lock_flags(lock, flags) arch_spin_lock(lock)
+
+static inline void arch_spin_lock(arch_spinlock_t *lock)
+{
+        unsigned int tmp;
+
+        asm volatile(
+        "       sevl\n"
+        "1:     wfe\n"
+        "2:     ldaxr   %w0, [%1]\n"
+        "       cbnz    %w0, 1b\n"
+        "       stxr    %w0, %w2, [%1]\n"
+        "       cbnz    %w0, 2b\n"
+        : "=&r" (tmp)
+        : "r" (&lock->lock), "r" (1)
+        : "memory");
+}
+
+static inline int arch_spin_trylock(arch_spinlock_t *lock)
+{
+        unsigned int tmp;
+
+        asm volatile(
+        "       ldaxr   %w0, [%1]\n"
+        "       cbnz    %w0, 1f\n"
+        "       stxr    %w0, %w2, [%1]\n"
+        "1:\n"
+        : "=&r" (tmp)
+        : "r" (&lock->lock), "r" (1)
+        : "memory");
+
+        return !tmp;
+}
+
+static inline void arch_spin_unlock(arch_spinlock_t *lock)
+{
+        asm volatile(
+        "       stlr    %w1, [%0]\n"
+        : : "r" (&lock->lock), "r" (0) : "memory");
+}
+
+/*
+ * Write lock implementation.
+ *
+ * Write locks set bit 31. Unlocking, is done by writing 0 since the lock is
+ * exclusively held.
+ *
+ * The memory barriers are implicit with the load-acquire and store-release
+ * instructions.
+ */
+
+static inline void arch_write_lock(arch_rwlock_t *rw)
+{
+        unsigned int tmp;
+
+        asm volatile(
+        "       sevl\n"
+        "1:     wfe\n"
+        "2:     ldaxr   %w0, [%1]\n"
+        "       cbnz    %w0, 1b\n"
+        "       stxr    %w0, %w2, [%1]\n"
+        "       cbnz    %w0, 2b\n"
+        : "=&r" (tmp)
+        : "r" (&rw->lock), "r" (0x80000000)
+        : "memory");
+}
+
+static inline int arch_write_trylock(arch_rwlock_t *rw)
+{
+        unsigned int tmp;
+
+        asm volatile(
+        "       ldaxr   %w0, [%1]\n"
+        "       cbnz    %w0, 1f\n"
+        "       stxr    %w0, %w2, [%1]\n"
+        "1:\n"
+        : "=&r" (tmp)
+        : "r" (&rw->lock), "r" (0x80000000)
+        : "memory");
+
+        return !tmp;
+}
+
+static inline void arch_write_unlock(arch_rwlock_t *rw)
+{
+        asm volatile(
+        "       stlr    %w1, [%0]\n"
+        : : "r" (&rw->lock), "r" (0) : "memory");
+}
+
+/* write_can_lock - would write_trylock() succeed? */
+#define arch_write_can_lock(x)          ((x)->lock == 0)
+
+/*
+ * Read lock implementation.
+ *
+ * It exclusively loads the lock value, increments it and stores the new value
+ * back if positive and the CPU still exclusively owns the location. If the
+ * value is negative, the lock is already held.
+ *
+ * During unlocking there may be multiple active read locks but no write lock.
+ *
+ * The memory barriers are implicit with the load-acquire and store-release
+ * instructions.
+ */
+static inline void arch_read_lock(arch_rwlock_t *rw)
+{
+        unsigned int tmp, tmp2;
+
+        asm volatile(
+        "       sevl\n"
+        "1:     wfe\n"
+        "2:     ldaxr   %w0, [%2]\n"
+        "       add     %w0, %w0, #1\n"
+        "       tbnz    %w0, #31, 1b\n"
+        "       stxr    %w1, %w0, [%2]\n"
+        "       cbnz    %w1, 2b\n"
+        : "=&r" (tmp), "=&r" (tmp2)
+        : "r" (&rw->lock)
+        : "memory");
+}
+
+static inline void arch_read_unlock(arch_rwlock_t *rw)
+{
+        unsigned int tmp, tmp2;
+
+        asm volatile(
+        "1:     ldxr    %w0, [%2]\n"
+        "       sub     %w0, %w0, #1\n"
+        "       stlxr   %w1, %w0, [%2]\n"
+        "       cbnz    %w1, 1b\n"
+        : "=&r" (tmp), "=&r" (tmp2)
+        : "r" (&rw->lock)
+        : "memory");
+}
+
+static inline int arch_read_trylock(arch_rwlock_t *rw)
+{
+        unsigned int tmp, tmp2 = 1;
+
+        asm volatile(
+        "       ldaxr   %w0, [%2]\n"
+        "       add     %w0, %w0, #1\n"
+        "       tbnz    %w0, #31, 1f\n"
+        "       stxr    %w1, %w0, [%2]\n"
+        "1:\n"
+        : "=&r" (tmp), "+r" (tmp2)
+        : "r" (&rw->lock)
+        : "memory");
+
+        return !tmp2;
+}
+
+/* read_can_lock - would read_trylock() succeed? */
+#define arch_read_can_lock(x)           ((x)->lock < 0x80000000)
+
+#define arch_read_lock_flags(lock, flags) arch_read_lock(lock)
+#define arch_write_lock_flags(lock, flags) arch_write_lock(lock)
+
+#define arch_spin_relax(lock)   cpu_relax()
+#define arch_read_relax(lock)   cpu_relax()
+#define arch_write_relax(lock)  cpu_relax()
+
+#endif /* __ASM_SPINLOCK_H */