[PATCH V9 14/15] openrisc: Move from ticket-lock to qspinlock

[guoren at kernel.org]

From: Guo Ren <guoren at linux.alibaba.com>

Enable qspinlock by the requirements mentioned in a8ad07e5240c9
("asm-generic: qspinlock: Indicate the use of mixed-size atomics").

Openrisc only has "l.lwa/l.swa" for all atomic operations. That means
its ll/sc pair should be a strong atomic forward progress guarantee, or
all atomic operations may cause live lock. The ticket-lock needs
atomic_fetch_add well defined forward progress guarantees under
contention, and qspinlock needs xchg16 forward progress guarantees. The
atomic_fetch_add (l.lwa + add + l.swa) & xchg16 (l.lwa + and + or +
l.swa) have similar implementations, so they has the same forward
progress guarantees.

The qspinlock is smaller and faster than ticket-lock when all is in
fast-path. No reason keep openrisc in ticket-lock not qspinlock. Here is
the comparison between qspinlock and ticket-lock in fast-path code
sizes (bytes):

TYPE			: TICKET | QUEUED
arch_spin_lock		: 128    | 96
arch_spin_unlock	: 56     | 44
arch_spin_trylock	: 108    | 80
arch_spin_is_locked	: 36     | 36
arch_spin_is_contended	: 36     | 36
arch_spin_value_unlocked: 28     | 28

Signed-off-by: Guo Ren <guoren at linux.alibaba.com>
Signed-off-by: Guo Ren <guoren at kernel.org>
Cc: Stafford Horne <shorne at gmail.com>
Cc: Jonas Bonn <jonas at southpole.se>
Cc: Stefan Kristiansson <stefan.kristiansson at saunalahti.fi>
---
 arch/openrisc/Kconfig               |  1 +
 arch/openrisc/include/asm/Kbuild    |  2 ++
 arch/openrisc/include/asm/cmpxchg.h | 25 +++++++++++++++++++++++++
 3 files changed, 28 insertions(+)

diff --git a/arch/openrisc/Kconfig b/arch/openrisc/Kconfig
index c7f282f60f64..1652a6aac882 100644
--- a/arch/openrisc/Kconfig
+++ b/arch/openrisc/Kconfig
@@ -10,6 +10,7 @@ config OPENRISC
 	select ARCH_HAS_DMA_SET_UNCACHED
 	select ARCH_HAS_DMA_CLEAR_UNCACHED
 	select ARCH_HAS_SYNC_DMA_FOR_DEVICE
+	select ARCH_USE_QUEUED_SPINLOCKS
 	select COMMON_CLK
 	select OF
 	select OF_EARLY_FLATTREE
diff --git a/arch/openrisc/include/asm/Kbuild b/arch/openrisc/include/asm/Kbuild
index c8c99b554ca4..ad147fec50b4 100644
--- a/arch/openrisc/include/asm/Kbuild
+++ b/arch/openrisc/include/asm/Kbuild
@@ -2,6 +2,8 @@
 generic-y += extable.h
 generic-y += kvm_para.h
 generic-y += parport.h
+generic-y += mcs_spinlock.h
+generic-y += qspinlock.h
 generic-y += spinlock_types.h
 generic-y += spinlock.h
 generic-y += qrwlock_types.h
diff --git a/arch/openrisc/include/asm/cmpxchg.h b/arch/openrisc/include/asm/cmpxchg.h
index df83b33b5882..2d650b07a0f4 100644
--- a/arch/openrisc/include/asm/cmpxchg.h
+++ b/arch/openrisc/include/asm/cmpxchg.h
@@ -65,6 +65,27 @@ static inline u32 cmpxchg32(volatile void *ptr, u32 old, u32 new)
 })
 
 /* xchg */
+static inline u32 xchg16(volatile void *ptr, u32 val)
+{
+	u32 ret, tmp;
+	u32 shif = ((ulong)ptr & 2) ? 16 : 0;
+	u32 mask = 0xffff << shif;
+	u32 *__ptr = (u32 *)((ulong)ptr & ~2);
+
+	__asm__ __volatile__(
+		"1:	l.lwa %0, 0(%2)		\n"
+		"	l.and %1, %0, %3	\n"
+		"	l.or  %1, %1, %4	\n"
+		"	l.swa 0(%2), %1		\n"
+		"	l.bnf 1b		\n"
+		"	 l.nop			\n"
+		: "=&r" (ret), "=&r" (tmp)
+		: "r"(__ptr), "r" (~mask), "r" (val << shif)
+		: "cc", "memory");
+
+	return (ret & mask) >> shif;
+}
+
 static inline u32 xchg32(volatile void *ptr, u32 val)
 {
 	__asm__ __volatile__(
@@ -85,6 +106,10 @@ static inline u32 xchg32(volatile void *ptr, u32 val)
 	__typeof__(new) __new = (new);					\
 	__typeof__(*(ptr)) __ret;					\
 	switch (size) {							\
+	case 2:								\
+		__ret = (__typeof__(*(ptr)))				\
+			xchg16(__ptr, (u32)__new);			\
+		break;							\
 	case 4:								\
 		__ret = (__typeof__(*(ptr)))				\
 			xchg32(__ptr, (u32)__new);			\
-- 
2.36.1