linux-kernel - [PATCH 09/17] m68k: Implement xor_unlock_is_negative

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Message-Id: <20230915183707.2707298-10-willy@infradead.org>
Date:   Fri, 15 Sep 2023 19:36:59 +0100
From:   "Matthew Wilcox (Oracle)" <willy@...radead.org>
To:     linux-kernel@...r.kernel.org
Cc:     "Matthew Wilcox (Oracle)" <willy@...radead.org>,
        linux-fsdevel@...r.kernel.org, linux-arch@...r.kernel.org,
        torvalds@...ux-foundation.org, Nicholas Piggin <npiggin@...il.com>
Subject: [PATCH 09/17] m68k: Implement xor_unlock_is_negative_byte

Using EOR to clear the guaranteed-to-be-set lock bit will test the
negative flag just like the x86 implementation.  This should be
more efficient than the generic implementation in filemap.c.  It
would be better if m68k had __GCC_ASM_FLAG_OUTPUTS__.

Signed-off-by: Matthew Wilcox (Oracle) <willy@...radead.org>
---
 arch/m68k/include/asm/bitops.h | 14 ++++++++++++++
 1 file changed, 14 insertions(+)

diff --git a/arch/m68k/include/asm/bitops.h b/arch/m68k/include/asm/bitops.h
index e984af71df6b..909ebe7cab5d 100644
--- a/arch/m68k/include/asm/bitops.h
+++ b/arch/m68k/include/asm/bitops.h
@@ -319,6 +319,20 @@ arch___test_and_change_bit(unsigned long nr, volatile unsigned long *addr)
 	return test_and_change_bit(nr, addr);
 }
 
+static inline bool xor_unlock_is_negative_byte(unsigned long mask,
+		volatile unsigned long *p)
+{
+	char result;
+	char *cp = (char *)p + 3;	/* m68k is big-endian */
+
+	__asm__ __volatile__ ("eor.b %1, %2; smi %0"
+		: "=d" (result)
+		: "di" (mask), "o" (*cp)
+		: "memory");
+	return result;
+}
+#define xor_unlock_is_negative_byte xor_unlock_is_negative_byte
+
 /*
  *	The true 68020 and more advanced processors support the "bfffo"
  *	instruction for finding bits. ColdFire and simple 68000 parts
-- 
2.40.1