[PATCH 08/17] alpha: Implement xor_unlock_is_negative_byte

Matthew Wilcox (Oracle)
2023-09-15T18:38:45Z

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..138930e8a504 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"
+ " xor %0,%3,%0\n"
+ " xor %0,%3,%2\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