linux-kernel - [PATCH 09/11] powerpc/8xx: dont save CR in SCRATCH registers

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Date:	Mon, 20 Apr 2015 07:26:41 +0200 (CEST)
From:	Christophe Leroy <christophe.leroy@....fr>
To:	Benjamin Herrenschmidt <benh@...nel.crashing.org>,
	Paul Mackerras <paulus@...ba.org>,
	Michael Ellerman <mpe@...erman.id.au>, scottwood@...escale.com
CC:	linux-kernel@...r.kernel.org, linuxppc-dev@...ts.ozlabs.org,
	Joakim Tjernlund <joakim.tjernlund@...nsmode.se>
Subject: [PATCH 09/11] powerpc/8xx: dont save CR in SCRATCH registers

CR only needs to be preserved when checking if we are handling a kernel address.
So we can preserve CR in a register:
- In ITLBMiss, check is done only when CONFIG_MODULES is defined. Otherwise we
don't need to do anything at all with CR.
- If CONFIG_8xx_CPU6 is defined, we have r3 available for saving CR
- Otherwise, we use r10, then we reload SRR0/MD_EPN into r10 when CR is restored

Signed-off-by: Christophe Leroy <christophe.leroy@....fr>

---
 arch/powerpc/kernel/head_8xx.S | 53 +++++++++++++++++++++++++++++-------------
 1 file changed, 37 insertions(+), 16 deletions(-)

diff --git a/arch/powerpc/kernel/head_8xx.S b/arch/powerpc/kernel/head_8xx.S
index c89aed9..a073918 100644
--- a/arch/powerpc/kernel/head_8xx.S
+++ b/arch/powerpc/kernel/head_8xx.S
@@ -308,14 +308,10 @@ SystemCall:
 #endif
 
 InstructionTLBMiss:
+	EXCEPTION_PROLOG_0
 #ifdef CONFIG_8xx_CPU6
 	mtspr	SPRN_DAR, r3
 #endif
-	EXCEPTION_PROLOG_0
-	mfcr	r10
-	mtspr	SPRN_SPRG_SCRATCH2, r10
-	mfspr	r10, SPRN_SRR0	/* Get effective address of fault */
-	DO_8xx_CPU15(r11, r10)
 
 	/* If we are faulting a kernel address, we have to use the
 	 * kernel page tables.
@@ -323,14 +319,33 @@ InstructionTLBMiss:
 #ifdef CONFIG_MODULES
 	/* Only modules will cause ITLB Misses as we always
 	 * pin the first 8MB of kernel memory */
+#ifdef CONFIG_8xx_CPU6
+	mfspr	r10, SPRN_SRR0	/* Get effective address of fault */
+	DO_8xx_CPU15(r11, r10)
+	mfcr	r3
 	andis.	r11, r10, 0x8000	/* Address >= 0x80000000 */
+#else
+	mfspr	r11, SPRN_SRR0	/* Get effective address of fault */
+	DO_8xx_CPU15(r10, r11)
+	mfcr	r10
+	andis.	r11, r11, 0x8000	/* Address >= 0x80000000 */
 #endif
 	mfspr	r11, SPRN_M_TW	/* Get level 1 table base address */
-#ifdef CONFIG_MODULES
 	beq	3f
 	lis	r11, (swapper_pg_dir-PAGE_OFFSET)@ha
 3:
+#ifdef CONFIG_8xx_CPU6
+	mtcr	r3
+#else
+	mtcr	r10
+	mfspr	r10, SPRN_SRR0	/* Get effective address of fault */
 #endif
+#else /* CONFIG_MODULES */
+	mfspr	r10, SPRN_SRR0	/* Get effective address of fault */
+	DO_8xx_CPU15(r11, r10)
+	mfspr	r11, SPRN_M_TW	/* Get level 1 table base address */
+#endif /* CONFIG_MODULES */
+
 	/* Insert level 1 index */
 	rlwimi	r11, r10, 32 - ((PAGE_SHIFT - 2) << 1), (PAGE_SHIFT - 2) << 1, 29
 	lwz	r11, (swapper_pg_dir-PAGE_OFFSET)@l(r11)	/* Get the level 1 entry */
@@ -362,29 +377,37 @@ InstructionTLBMiss:
 	mfspr	r3, SPRN_DAR
 	mtspr	SPRN_DAR, r11	/* Tag DAR */
 #endif
-	mfspr	r10, SPRN_SPRG_SCRATCH2
-	mtcr	r10
 	EXCEPTION_EPILOG_0
 	rfi
 
 	. = 0x1200
 DataStoreTLBMiss:
-#ifdef CONFIG_8xx_CPU6
-	mtspr	SPRN_DAR, r3
-#endif
 	EXCEPTION_PROLOG_0
-	mfcr	r10
-	mtspr	SPRN_SPRG_SCRATCH2, r10
-	mfspr	r10, SPRN_MD_EPN
 
 	/* If we are faulting a kernel address, we have to use the
 	 * kernel page tables.
 	 */
+#ifdef CONFIG_8xx_CPU6
+	mtspr	SPRN_DAR, r3
+	mfcr	r3
+	mfspr	r10, SPRN_MD_EPN
 	andis.	r11, r10, 0x8000
+#else
+	mfcr	r10
+	mfspr	r11, SPRN_MD_EPN
+	andis.	r11, r11, 0x8000
+#endif
 	mfspr	r11, SPRN_M_TW	/* Get level 1 table base address */
 	beq	3f
 	lis	r11, (swapper_pg_dir-PAGE_OFFSET)@ha
 3:
+#ifdef CONFIG_8xx_CPU6
+	mtcr	r3
+#else
+	mtcr	r10
+	mfspr	r10, SPRN_MD_EPN
+#endif
+
 	/* Insert level 1 index */
 	rlwimi	r11, r10, 32 - ((PAGE_SHIFT - 2) << 1), (PAGE_SHIFT - 2) << 1, 29
 	lwz	r11, (swapper_pg_dir-PAGE_OFFSET)@l(r11)	/* Get the level 1 entry */
@@ -441,8 +464,6 @@ DataStoreTLBMiss:
 	mfspr	r3, SPRN_DAR
 #endif
 	mtspr	SPRN_DAR, r11	/* Tag DAR */
-	mfspr	r10, SPRN_SPRG_SCRATCH2
-	mtcr	r10
 	EXCEPTION_EPILOG_0
 	rfi
 
-- 
2.1.0

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