[PATCH v2 08/17] alpha: Implement xor_unlock_is_negative_byte

["Matthew Wilcox (Oracle)" <willy@infradead.org>]

Inspired by the alpha clear_bit() and arch_atomic_add_return(), this
will surely be more efficient than the generic one defined in filemap.c.

Signed-off-by: Matthew Wilcox (Oracle) <willy@infradead.org>
---
 arch/alpha/include/asm/bitops.h | 21 +++++++++++++++++++++
 1 file changed, 21 insertions(+)

diff --git a/arch/alpha/include/asm/bitops.h b/arch/alpha/include/asm/bitops.h
index bafb1c1f0fdc..b50ad6b83e85 100644
--- a/arch/alpha/include/asm/bitops.h
+++ b/arch/alpha/include/asm/bitops.h
@@ -286,6 +286,27 @@ arch___test_and_change_bit(unsigned long nr, volatile unsigned long *addr)
 #define arch_test_bit generic_test_bit
 #define arch_test_bit_acquire generic_test_bit_acquire
 
+static inline bool xor_unlock_is_negative_byte(unsigned long mask,
+		volatile unsigned long *p)
+{
+	unsigned long temp, old;
+
+	__asm__ __volatile__(
+	"1:	ldl_l %0,%4\n"
+	"	mov %0,%2\n"
+	"	xor %0,%3,%0\n"
+	"	stl_c %0,%1\n"
+	"	beq %0,2f\n"
+	".subsection 2\n"
+	"2:	br 1b\n"
+	".previous"
+	:"=&r" (temp), "=m" (*p), "=&r" (old)
+	:"Ir" (mask), "m" (*p));
+
+	return (old & BIT(7)) != 0;
+}
+#define xor_unlock_is_negative_byte xor_unlock_is_negative_byte
+
 /*
  * ffz = Find First Zero in word. Undefined if no zero exists,
  * so code should check against ~0UL first..
-- 
2.40.1