mips: implement xor_unlock_is_negative_byte

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

Link: https://lkml.kernel.org/r/[email protected]
Signed-off-by: Matthew Wilcox (Oracle) <[email protected]>
Cc: Albert Ou <[email protected]>
Cc: Alexander Gordeev <[email protected]>
Cc: Andreas Dilger <[email protected]>
Cc: Christian Borntraeger <[email protected]>
Cc: Christophe Leroy <[email protected]>
Cc: Geert Uytterhoeven <[email protected]>
Cc: Heiko Carstens <[email protected]>
Cc: Ivan Kokshaysky <[email protected]>
Cc: Matt Turner <[email protected]>
Cc: Michael Ellerman <[email protected]>
Cc: Nicholas Piggin <[email protected]>
Cc: Palmer Dabbelt <[email protected]>
Cc: Paul Walmsley <[email protected]>
Cc: Richard Henderson <[email protected]>
Cc: Sven Schnelle <[email protected]>
Cc: "Theodore Ts'o" <[email protected]>
Cc: Thomas Bogendoerfer <[email protected]>
Cc: Vasily Gorbik <[email protected]>
Signed-off-by: Andrew Morton <[email protected]>

Author: Matthew Wilcox (Oracle)

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
 

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;
+}