[PATCH 2/2] [RFCv3] arm: add half-word __xchg
Alexander Shishkin
virtuoso at slind.org
Sat May 1 15:24:57 EDT 2010
On systems where ldrexh/strexh are not available,
* for pre-v6 systems, use a generic local version,
* for v6 without v6K, emulate xchg2 using 32-bit cmpxchg()
(it is not yet clear if xchg1 has to be emulated on such
systems as well, thus the "size" parameter).
The __xchg_generic() function is based on the code that Jamie
posted earlier.
Signed-off-by: Alexander Shishkin <virtuoso at slind.org>
CC: linux-arm-kernel-bounces at lists.infradead.org
CC: Imre Deak <imre.deak at nokia.com>
CC: Mathieu Desnoyers <mathieu.desnoyers at polymtl.ca>
CC: Jamie Lokier <jamie at shareable.org>
---
arch/arm/include/asm/system.h | 56 +++++++++++++++++++++++++++++++++++++++++
1 files changed, 56 insertions(+), 0 deletions(-)
diff --git a/arch/arm/include/asm/system.h b/arch/arm/include/asm/system.h
index d65b2f5..7a5983f 100644
--- a/arch/arm/include/asm/system.h
+++ b/arch/arm/include/asm/system.h
@@ -218,6 +218,39 @@ do { \
last = __switch_to(prev,task_thread_info(prev), task_thread_info(next)); \
} while (0)
+#if __LINUX_ARM_ARCH__ >= 6
+
+#include <linux/align.h>
+
+static inline unsigned long __cmpxchg(volatile void *ptr, unsigned long old,
+ unsigned long new, int size);
+
+/*
+ * emulate __xchg() using 32-bit __cmpxchg()
+ */
+static inline unsigned long __xchg_generic(unsigned long x,
+ volatile void *ptr, int size)
+{
+ unsigned long *ptrbig = object_align_floor((unsigned long *)ptr);
+ int shift = ((unsigned)ptr - (unsigned)ptrbig) * 8;
+ unsigned long mask, add, ret;
+
+ mask = ~(((1 << (size * 8)) - 1) << shift);
+ add = x << shift;
+
+ ret = *ptrbig;
+ while (1) {
+ unsigned long tmp = __cmpxchg(ptrbig, ret, (ret & mask) | add,
+ 4);
+ if (tmp == ret)
+ break;
+ ret = tmp;
+ }
+
+ return ret;
+}
+#endif
+
#if defined(CONFIG_CPU_SA1100) || defined(CONFIG_CPU_SA110)
/*
* On the StrongARM, "swp" is terminally broken since it bypasses the
@@ -262,6 +295,22 @@ static inline unsigned long __xchg(unsigned long x, volatile void *ptr, int size
: "r" (x), "r" (ptr)
: "memory", "cc");
break;
+#ifdef CONFIG_CPU_32v6K
+ case 2:
+ asm volatile("@ __xchg2\n"
+ "1: ldrexh %0, [%3]\n"
+ " strexh %1, %2, [%3]\n"
+ " teq %1, #0\n"
+ " bne 1b"
+ : "=&r" (ret), "=&r" (tmp)
+ : "r" (x), "r" (ptr)
+ : "memory", "cc");
+ break;
+#else
+ case 2:
+ ret = __xchg_generic(x, ptr, 2);
+ break;
+#endif
case 4:
asm volatile("@ __xchg4\n"
"1: ldrex %0, [%3]\n"
@@ -283,6 +332,13 @@ static inline unsigned long __xchg(unsigned long x, volatile void *ptr, int size
raw_local_irq_restore(flags);
break;
+ case 2:
+ raw_local_irq_save(flags);
+ ret = *(volatile unsigned short *)ptr;
+ *(volatile unsigned short *)ptr = x;
+ raw_local_irq_restore(flags);
+ break;
+
case 4:
raw_local_irq_save(flags);
ret = *(volatile unsigned long *)ptr;
--
1.7.1.1.g15764
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