[Skiboot] [RFC PATCH 1/3] core/lock: Introduce atomic cmpxchg and implement try_lock with it

[Nicholas Piggin]

---
 asm/Makefile.inc |  2 +-
 asm/lock.S       | 43 -------------------------------------------
 core/lock.c      | 26 ++++++++++++++++++++++----
 include/lock.h   | 46 ++++++++++++++++++++++++++++++++++++++++++++--
 4 files changed, 67 insertions(+), 50 deletions(-)
 delete mode 100644 asm/lock.S

diff --git a/asm/Makefile.inc b/asm/Makefile.inc
index 2e678fd8..34e2b288 100644
--- a/asm/Makefile.inc
+++ b/asm/Makefile.inc
@@ -1,7 +1,7 @@
 # -*-Makefile-*-
 
 SUBDIRS += asm 
-ASM_OBJS = head.o lock.o misc.o kernel-wrapper.o rom_entry.o
+ASM_OBJS = head.o misc.o kernel-wrapper.o rom_entry.o
 ASM=asm/built-in.o
 
 # Add extra dependency to the kernel wrapper
diff --git a/asm/lock.S b/asm/lock.S
deleted file mode 100644
index ce28010f..00000000
--- a/asm/lock.S
+++ /dev/null
@@ -1,43 +0,0 @@
-/* Copyright 2013-2014 IBM Corp.
- *
- * Licensed under the Apache License, Version 2.0 (the "License");
- * you may not use this file except in compliance with the License.
- * You may obtain a copy of the License at
- *
- * 	http://www.apache.org/licenses/LICENSE-2.0
- *
- * Unless required by applicable law or agreed to in writing, software
- * distributed under the License is distributed on an "AS IS" BASIS,
- * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or
- * implied.
- * See the License for the specific language governing permissions and
- * limitations under the License.
- */
-
-#include <asm-utils.h>
-#include <asm-offsets.h>
-#include <processor.h>
-
-	.section ".text","ax"
-	.balign	0x10
-
-	/* bool try_lock(struct lock *lock) */
-.global __try_lock
-__try_lock:
-	ld	%r0,0(%r3)
-	andi.	%r10,%r0,1
-	bne	2f
-	lwz	%r9,CPUTHREAD_PIR(%r13)
-1:	ldarx	%r0,0,%r3
-	andi.	%r10,%r0,1
-	bne-	2f
-	ori	%r0,%r0,1
-	rldimi	%r0,%r9,32,0
-	stdcx.	%r0,0,%r3
-	bne	1b
-	sync
-	li	%r3,-1
-	blr
-2:	li	%r3,0
-	blr
-
diff --git a/core/lock.c b/core/lock.c
index 0868f2ba..916a0241 100644
--- a/core/lock.c
+++ b/core/lock.c
@@ -33,7 +33,7 @@ static void lock_error(struct lock *l, const char *reason, uint16_t err)
 {
 	bust_locks = true;
 
-	fprintf(stderr, "LOCK ERROR: %s @%p (state: 0x%016lx)\n",
+	fprintf(stderr, "LOCK ERROR: %s @%p (state: 0x%016llx)\n",
 		reason, l, l->lock_val);
 	op_display(OP_FATAL, OP_MOD_LOCK, err);
 
@@ -73,12 +73,30 @@ bool lock_held_by_me(struct lock *l)
 	return l->lock_val == ((pir64 << 32) | 1);
 }
 
+static inline bool __try_lock(struct cpu_thread *cpu, struct lock *l)
+{
+	uint64_t val;
+
+	val = cpu->pir;
+	val <<= 32;
+	val |= 1;
+
+	barrier();
+	if (__cmpxchg64(&l->lock_val, 0, val) == 0) {
+		sync();
+		return true;
+	}
+	return false;
+}
+
 bool try_lock(struct lock *l)
 {
-	if (__try_lock(l)) {
+	struct cpu_thread *cpu = this_cpu();
+
+	if (__try_lock(cpu, l)) {
 		if (l->in_con_path)
-			this_cpu()->con_suspend++;
-		this_cpu()->lock_depth++;
+			cpu->con_suspend++;
+		cpu->lock_depth++;
 		return true;
 	}
 	return false;
diff --git a/include/lock.h b/include/lock.h
index 0ac943dc..b42afaa4 100644
--- a/include/lock.h
+++ b/include/lock.h
@@ -23,7 +23,7 @@ struct lock {
 	/* Lock value has bit 63 as lock bit and the PIR of the owner
 	 * in the top 32-bit
 	 */
-	unsigned long lock_val;
+	uint64_t lock_val;
 
 	/*
 	 * Set to true if lock is involved in the console flush path
@@ -63,7 +63,49 @@ static inline void init_lock(struct lock *l)
 	*l = (struct lock)LOCK_UNLOCKED;
 }
 
-extern bool __try_lock(struct lock *l);
+/*
+ * Bare cmpxchg, no barriers.
+ */
+static inline uint32_t __cmpxchg32(uint32_t *mem, uint32_t old, uint32_t new)
+{
+	uint32_t prev;
+
+	asm volatile(
+		"# __cmpxchg32		\n"
+		"1:	lwarx	%0,0,%2	\n"
+		"	cmpw	%0,%3	\n"
+		"	bne-	2f	\n"
+		"	stwcx.	%4,0,%2	\n"
+		"	bne-	1b	\n"
+		"2:			\n"
+
+		: "=&r"(prev), "+m"(*mem)
+		: "r"(mem), "r"(old), "r"(new)
+		: "cr0");
+
+	return prev;
+}
+
+static inline uint64_t __cmpxchg64(uint64_t *mem, uint64_t old, uint64_t new)
+{
+	uint64_t prev;
+
+	asm volatile(
+		"# __cmpxchg64		\n"
+		"1:	ldarx	%0,0,%2	\n"
+		"	cmpd	%0,%3	\n"
+		"	bne-	2f	\n"
+		"	stdcx.	%4,0,%2	\n"
+		"	bne-	1b	\n"
+		"2:			\n"
+
+		: "=&r"(prev), "+m"(*mem)
+		: "r"(mem), "r"(old), "r"(new)
+		: "cr0");
+
+	return prev;
+}
+
 extern bool try_lock(struct lock *l);
 extern void lock(struct lock *l);
 extern void unlock(struct lock *l);
-- 
2.13.3