From: Will Deacon <will.deacon@arm.com>
Date: Wed, 9 Jul 2014 18:31:28 +0000 (+0100)
Subject: ARM: 8098/1: mcs lock: implement wfe-based polling for MCS locking
X-Git-Tag: firefly_0821_release~176^2~3485^2~2^2~12
X-Git-Url: http://demsky.eecs.uci.edu/git/?a=commitdiff_plain;h=bf67fd3142dc605ded9b5e063e35b47c2bb21cb1;p=firefly-linux-kernel-4.4.55.git

ARM: 8098/1: mcs lock: implement wfe-based polling for MCS locking

This patch introduces a wfe-based polling loop for spinning on contended
MCS locks and waking up corresponding waiters when the lock is released.

Signed-off-by: Will Deacon <will.deacon@arm.com>
Signed-off-by: Russell King <rmk+kernel@arm.linux.org.uk>
---

diff --git a/arch/arm/include/asm/mcs_spinlock.h b/arch/arm/include/asm/mcs_spinlock.h
new file mode 100644
index 000000000000..f652ad65840a
--- /dev/null
+++ b/arch/arm/include/asm/mcs_spinlock.h
@@ -0,0 +1,23 @@
+#ifndef __ASM_MCS_LOCK_H
+#define __ASM_MCS_LOCK_H
+
+#ifdef CONFIG_SMP
+#include <asm/spinlock.h>
+
+/* MCS spin-locking. */
+#define arch_mcs_spin_lock_contended(lock)				\
+do {									\
+	/* Ensure prior stores are observed before we enter wfe. */	\
+	smp_mb();							\
+	while (!(smp_load_acquire(lock)))				\
+		wfe();							\
+} while (0)								\
+
+#define arch_mcs_spin_unlock_contended(lock)				\
+do {									\
+	smp_store_release(lock, 1);					\
+	dsb_sev();							\
+} while (0)
+
+#endif	/* CONFIG_SMP */
+#endif	/* __ASM_MCS_LOCK_H */