linux-kernel - [PATCH 18/37] MIPS: bitops: Only use ins for bit 16 or higher

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Date:   Mon, 30 Sep 2019 23:08:29 +0000
From:   Paul Burton <paul.burton@...s.com>
To:     "linux-mips@...r.kernel.org" <linux-mips@...r.kernel.org>
CC:     Huacai Chen <chenhc@...ote.com>,
        Jiaxun Yang <jiaxun.yang@...goat.com>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        Paul Burton <pburton@...ecomp.com>
Subject: [PATCH 18/37] MIPS: bitops: Only use ins for bit 16 or higher

set_bit() can set bits 0-15 using an ori instruction, rather than
loading the value -1 into a register & then using an ins instruction.

That is, rather than the following:

  li   t0, -1
  ll   t1, 0(t2)
  ins  t1, t0, 4, 1
  sc   t1, 0(t2)

We can have the simpler:

  ll   t1, 0(t2)
  ori  t1, t1, 0x10
  sc   t1, 0(t2)

The or path already allows immediates to be used, so simply restricting
the ins path to bits that don't fit in immediates is sufficient to take
advantage of this.

Signed-off-by: Paul Burton <paul.burton@...s.com>
---

 arch/mips/include/asm/bitops.h | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/arch/mips/include/asm/bitops.h b/arch/mips/include/asm/bitops.h
index d3f3f37ca0b1..3ea4f172ac08 100644
--- a/arch/mips/include/asm/bitops.h
+++ b/arch/mips/include/asm/bitops.h
@@ -77,7 +77,7 @@ static inline void set_bit(unsigned long nr, volatile unsigned long *addr)
 	}
 
 #if defined(CONFIG_CPU_MIPSR2) || defined(CONFIG_CPU_MIPSR6)
-	if (__builtin_constant_p(bit)) {
+	if (__builtin_constant_p(bit) && (bit >= 16)) {
 		loongson_llsc_mb();
 		do {
 			__asm__ __volatile__(
-- 
2.23.0