linux-kernel - [PATCH v2] powerpc/mm: Add mask of always present MMU features

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Message-Id: <06bf0e094463533e7aec6900bddd435171e9f44f.1602517171.git.christophe.leroy@csgroup.eu>
Date:   Mon, 12 Oct 2020 15:39:45 +0000 (UTC)
From:   Christophe Leroy <christophe.leroy@...roup.eu>
To:     Benjamin Herrenschmidt <benh@...nel.crashing.org>,
        Paul Mackerras <paulus@...ba.org>,
        Michael Ellerman <mpe@...erman.id.au>
Cc:     linux-kernel@...r.kernel.org, linuxppc-dev@...ts.ozlabs.org
Subject: [PATCH v2] powerpc/mm: Add mask of always present MMU features

On the same principle as commit 773edeadf672 ("powerpc/mm: Add mask
of possible MMU features"), add mask for MMU features that are
always there in order to optimise out dead branches.

Signed-off-by: Christophe Leroy <christophe.leroy@...roup.eu>
---
v2: Features must be anded with MMU_FTRS_POSSIBLE instead of ~0, otherwise
    MMU_FTRS_ALWAYS is ~0 when no #ifdef matches.
---
 arch/powerpc/include/asm/mmu.h | 25 +++++++++++++++++++++++++
 1 file changed, 25 insertions(+)

diff --git a/arch/powerpc/include/asm/mmu.h b/arch/powerpc/include/asm/mmu.h
index 255a1837e9f7..64e7e7f7cda9 100644
--- a/arch/powerpc/include/asm/mmu.h
+++ b/arch/powerpc/include/asm/mmu.h
@@ -201,8 +201,30 @@ enum {
 		0,
 };
 
+enum {
+	MMU_FTRS_ALWAYS =
+#ifdef CONFIG_PPC_8xx
+		MMU_FTR_TYPE_8xx &
+#endif
+#ifdef CONFIG_40x
+		MMU_FTR_TYPE_40x &
+#endif
+#ifdef CONFIG_PPC_47x
+		MMU_FTR_TYPE_47x &
+#elif defined(CONFIG_44x)
+		MMU_FTR_TYPE_44x &
+#endif
+#if defined(CONFIG_E200) || defined(CONFIG_E500)
+		MMU_FTR_TYPE_FSL_E &
+#endif
+		MMU_FTRS_POSSIBLE,
+};
+
 static inline bool early_mmu_has_feature(unsigned long feature)
 {
+	if (MMU_FTRS_ALWAYS & feature)
+		return true;
+
 	return !!(MMU_FTRS_POSSIBLE & cur_cpu_spec->mmu_features & feature);
 }
 
@@ -231,6 +253,9 @@ static __always_inline bool mmu_has_feature(unsigned long feature)
 	}
 #endif
 
+	if (MMU_FTRS_ALWAYS & feature)
+		return true;
+
 	if (!(MMU_FTRS_POSSIBLE & feature))
 		return false;
 
-- 
2.25.0