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From:   Christophe Leroy <christophe.leroy@csgroup.eu>
Subject: [PATCH 3/3] powerpc/32s: Allow constant folding in mtsr()/mfsr()
To:     Benjamin Herrenschmidt <benh@kernel.crashing.org>,
        Paul Mackerras <paulus@samba.org>,
        Michael Ellerman <mpe@ellerman.id.au>
Cc:     linux-kernel@vger.kernel.org, linuxppc-dev@lists.ozlabs.org
Date:   Sat,  6 Feb 2021 11:47:28 +0000 (UTC)
Precedence: bulk

On the same way as we did in wrtee(), add an alternative
using mtsr/mfsr instructions instead of mtsrin/mfsrin
when the segment register can be determined at compile time.

Signed-off-by: Christophe Leroy <christophe.leroy@csgroup.eu>
---
 arch/powerpc/include/asm/reg.h | 10 ++++++++--
 1 file changed, 8 insertions(+), 2 deletions(-)

diff --git a/arch/powerpc/include/asm/reg.h b/arch/powerpc/include/asm/reg.h
index eeab7e7dc699..da103e92c112 100644
--- a/arch/powerpc/include/asm/reg.h
+++ b/arch/powerpc/include/asm/reg.h
@@ -1418,14 +1418,20 @@ static inline u32 mfsr(u32 idx)
 {
 	u32 val;
 
-	asm volatile("mfsrin %0, %1" : "=r" (val): "r" (idx));
+	if (__builtin_constant_p(idx))
+		asm volatile("mfsr %0, %1" : "=r" (val): "i" (idx >> 28));
+	else
+		asm volatile("mfsrin %0, %1" : "=r" (val): "r" (idx));
 
 	return val;
 }
 
 static inline void mtsr(u32 val, u32 idx)
 {
-	asm volatile("mtsrin %0, %1" : : "r" (val), "r" (idx));
+	if (__builtin_constant_p(idx))
+		asm volatile("mtsr %1, %0" : : "r" (val), "i" (idx >> 28));
+	else
+		asm volatile("mtsrin %0, %1" : : "r" (val), "r" (idx));
 }
 #endif
 
-- 
2.25.0