From 8da36b26e3d8640364a9e60e0b5c3fa3f55d298b Mon Sep 17 00:00:00 2001
From: "Matthew Wilcox (Oracle)" <willy@infradead.org>
Date: Wed, 4 Oct 2023 17:53:10 +0100
Subject: [PATCH] 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/20231004165317.1061855-11-willy@infradead.org
Signed-off-by: Matthew Wilcox (Oracle) <willy@infradead.org>
Cc: Albert Ou <aou@eecs.berkeley.edu>
Cc: Alexander Gordeev <agordeev@linux.ibm.com>
Cc: Andreas Dilger <adilger.kernel@dilger.ca>
Cc: Christian Borntraeger <borntraeger@linux.ibm.com>
Cc: Christophe Leroy <christophe.leroy@csgroup.eu>
Cc: Geert Uytterhoeven <geert@linux-m68k.org>
Cc: Heiko Carstens <hca@linux.ibm.com>
Cc: Ivan Kokshaysky <ink@jurassic.park.msu.ru>
Cc: Matt Turner <mattst88@gmail.com>
Cc: Michael Ellerman <mpe@ellerman.id.au>
Cc: Nicholas Piggin <npiggin@gmail.com>
Cc: Palmer Dabbelt <palmer@dabbelt.com>
Cc: Paul Walmsley <paul.walmsley@sifive.com>
Cc: Richard Henderson <richard.henderson@linaro.org>
Cc: Sven Schnelle <svens@linux.ibm.com>
Cc: "Theodore Ts'o" <tytso@mit.edu>
Cc: Thomas Bogendoerfer <tsbogend@alpha.franken.de>
Cc: Vasily Gorbik <gor@linux.ibm.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.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;
+}