linux-kernel - [PATCH] powerpc/603: Avoid a pile of NOPs when not using SW LRU in TLB exceptions

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Message-Id: <603725297466959419628ef7964aaf3417fb647d.1620363691.git.christophe.leroy@csgroup.eu>
Date:   Fri,  7 May 2021 05:02:02 +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] powerpc/603: Avoid a pile of NOPs when not using SW LRU in
 TLB exceptions

The SW LRU is in an MMU feature section. When not used, that's a
dozen of NOPs to fetch for nothing.

Define an ALT section that does the few remaining operations.

That also avoids a double read on SRR1 in the SW LRU case.

Signed-off-by: Christophe Leroy <christophe.leroy@...roup.eu>
---
 arch/powerpc/kernel/head_book3s_32.S | 18 ++++++++++++++----
 1 file changed, 14 insertions(+), 4 deletions(-)

diff --git a/arch/powerpc/kernel/head_book3s_32.S b/arch/powerpc/kernel/head_book3s_32.S
index 065178f19a3d..f2a5ceff52b2 100644
--- a/arch/powerpc/kernel/head_book3s_32.S
+++ b/arch/powerpc/kernel/head_book3s_32.S
@@ -518,8 +518,6 @@ BEGIN_FTR_SECTION
 	rlwinm	r1,r1,0,~_PAGE_COHERENT	/* clear M (coherence not required) */
 END_FTR_SECTION_IFCLR(CPU_FTR_NEED_COHERENT)
 	mtspr	SPRN_RPA,r1
-	mfspr	r2,SPRN_SRR1		/* Need to restore CR0 */
-	mtcrf	0x80,r2
 BEGIN_MMU_FTR_SECTION
 	li	r0,1
 	mfspr	r1,SPRN_SPRG_603_LRU
@@ -531,9 +529,15 @@ BEGIN_MMU_FTR_SECTION
 	mfspr	r2,SPRN_SRR1
 	rlwimi	r2,r0,31-14,14,14
 	mtspr   SPRN_SRR1,r2
-END_MMU_FTR_SECTION_IFSET(MMU_FTR_NEED_DTLB_SW_LRU)
+	mtcrf	0x80,r2
+	tlbld	r3
+	rfi
+MMU_FTR_SECTION_ELSE
+	mfspr	r2,SPRN_SRR1		/* Need to restore CR0 */
+	mtcrf	0x80,r2
 	tlbld	r3
 	rfi
+ALT_MMU_FTR_SECTION_END_IFSET(MMU_FTR_NEED_DTLB_SW_LRU)
 DataAddressInvalid:
 	mfspr	r3,SPRN_SRR1
 	rlwinm	r1,r3,9,6,6	/* Get load/store bit */
@@ -607,9 +611,15 @@ BEGIN_MMU_FTR_SECTION
 	mfspr	r2,SPRN_SRR1
 	rlwimi	r2,r0,31-14,14,14
 	mtspr   SPRN_SRR1,r2
-END_MMU_FTR_SECTION_IFSET(MMU_FTR_NEED_DTLB_SW_LRU)
+	mtcrf	0x80,r2
+	tlbld	r3
+	rfi
+MMU_FTR_SECTION_ELSE
+	mfspr	r2,SPRN_SRR1		/* Need to restore CR0 */
+	mtcrf	0x80,r2
 	tlbld	r3
 	rfi
+ALT_MMU_FTR_SECTION_END_IFSET(MMU_FTR_NEED_DTLB_SW_LRU)
 
 #ifndef CONFIG_ALTIVEC
 #define altivec_assist_exception	unknown_exception
-- 
2.25.0