[PATCH 10/17] mips: Implement xor_unlock_is_negative_byte

Matthew Wilcox (Oracle)
2023-09-15T18:38:18Z

Inspired by the mips test_and_change_bit(), this will surely be more
efficient than the generic one defined in filemap.c

Signed-off-by: Matthew Wilcox (Oracle) <willy@infradead.org>
---
arch/mips/include/asm/bitops.h | 26 +++++++++++++++++++++++++-
arch/mips/lib/bitops.c | 14 ++++++++++++++
2 files changed, 39 insertions(+), 1 deletion(-)

diff --git a/arch/mips/include/asm/bitops.h b/arch/mips/include/asm/bitops.h
index b4bf754f7db3..d98a05c478f4 100644
--- a/arch/mips/include/asm/bitops.h
+++ b/arch/mips/include/asm/bitops.h
@@ -73,7 +73,8 @@ int __mips_test_and_clear_bit(unsigned long nr,
volatile unsigned long *addr);
int __mips_test_and_change_bit(unsigned long nr,
volatile unsigned long *addr);
-
+bool __mips_xor_is_negative_byte(unsigned long mask,
+ volatile unsigned long *addr);

/*
* set_bit - Atomically set a bit in memory
@@ -279,6 +280,29 @@ static inline int test_and_change_bit(unsigned long nr,
return res;
}

+static inline bool xor_unlock_is_negative_byte(unsigned long mask,
+ volatile unsigned long *p)
+{
+ unsigned long orig;
+ bool res;
+
+ smp_mb__before_atomic();
+
+ if (!kernel_uses_llsc) {
+ res = __mips_xor_is_negative_byte(mask, p);
+ } else {
+ orig = __test_bit_op(*p, "%0",
+ "xor\t%1, %0, %3",
+ "ir"(mask));
+ res = (orig & BIT(7)) != 0;
+ }
+
+ smp_llsc_mb();
+
+ return res;
+}
+#define xor_unlock_is_negative_byte xor_unlock_is_negative_byte
+
#undef __bit_op
#undef __test_bit_op

diff --git a/arch/mips/lib/bitops.c b/arch/mips/lib/bitops.c
index 116d0bd8b2ae..00aee98e9d54 100644
--- a/arch/mips/lib/bitops.c
+++ b/arch/mips/lib/bitops.c
@@ -146,3 +146,17 @@ int __mips_test_and_change_bit(unsigned long nr, volatile unsigned long *addr)
return res;
}
EXPORT_SYMBOL(__mips_test_and_change_bit);
+
+bool __mips_xor_is_negative_byte(unsigned long mask,
+ volatile unsigned long *addr)
+{
+ unsigned long flags;
+ unsigned long data;
+
+ raw_local_irq_save(flags);
+ data = *addr;
+ *addr = data ^ mask;
+ raw_local_irq_restore(flags);
+
+ return (data & BIT(7)) != 0;
+}
--
2.40.1