powerpc/40x: Avoid using r12 in TLB miss handlers

Let's reduce the number of registers used in TLB miss handlers.

We have both r9 and r12 available for any temporary use.

r9 is enough, avoid using r12.
Signed-off-by: Christophe Leroy <christophe.leroy@c-s.fr>
Signed-off-by: Christophe Leroy <christophe.leroy@csgroup.eu>
Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>
Link: https://lore.kernel.org/r/7f330e971952abb2645fb9ca4310c0f527e84dcb.1590079969.git.christophe.leroy@csgroup.eu

arch/powerpc/kernel/head_40x.S

@@ -255,9 +255,9 @@ _ENTRY(saved_ksp_limit)
 	mtspr	SPRN_SPRG_SCRATCH3, r12
 	mtspr	SPRN_SPRG_SCRATCH4, r9
 	mfcr	r11
-	mfspr	r12, SPRN_PID
+	mfspr	r9, SPRN_PID
 	mtspr	SPRN_SPRG_SCRATCH6, r11
-	mtspr	SPRN_SPRG_SCRATCH5, r12
+	mtspr	SPRN_SPRG_SCRATCH5, r9
 	mfspr	r10, SPRN_DEAR		/* Get faulting address */
 
 	/* If we are faulting a kernel address, we have to use the
@@ -280,12 +280,12 @@ _ENTRY(saved_ksp_limit)
 4:
 	tophys(r11, r11)
 	rlwimi	r11, r10, 12, 20, 29	/* Create L1 (pgdir/pmd) address */
-	lwz	r12, 0(r11)		/* Get L1 entry */
-	andi.	r9, r12, _PMD_PRESENT	/* Check if it points to a PTE page */
+	lwz	r11, 0(r11)		/* Get L1 entry */
+	andi.	r9, r11, _PMD_PRESENT	/* Check if it points to a PTE page */
 	beq	2f			/* Bail if no table */
 
-	rlwimi	r12, r10, 22, 20, 29	/* Compute PTE address */
-	lwz	r11, 0(r12)		/* Get Linux PTE */
+	rlwimi	r11, r10, 22, 20, 29	/* Compute PTE address */
+	lwz	r11, 0(r11)		/* Get Linux PTE */
 #ifdef CONFIG_SWAP
 	li	r9, _PAGE_PRESENT | _PAGE_ACCESSED
 #else
@@ -301,13 +301,13 @@ _ENTRY(saved_ksp_limit)
 	/* Create TLB tag.  This is the faulting address plus a static
 	 * set of bits.  These are size, valid, E, U0.
 	*/
-	li	r12, 0x00c0
-	rlwimi	r10, r12, 0, 20, 31
+	li	r9, 0x00c0
+	rlwimi	r10, r9, 0, 20, 31
 
 	b	finish_tlb_load
 
 2:	/* Check for possible large-page pmd entry */
-	rlwinm.	r9, r12, 2, 22, 24
+	rlwinm.	r9, r11, 2, 22, 24
 	beq	5f
 
 	/* Create TLB tag.  This is the faulting address, plus a static
@@ -315,7 +315,6 @@ _ENTRY(saved_ksp_limit)
 	 */
 	ori	r9, r9, 0x40
 	rlwimi	r10, r9, 0, 20, 31
-	mr	r11, r12
 
 	b	finish_tlb_load
 
@@ -323,9 +322,9 @@ _ENTRY(saved_ksp_limit)
 	/* The bailout.  Restore registers to pre-exception conditions
 	 * and call the heavyweights to help us out.
 	 */
-	mfspr	r12, SPRN_SPRG_SCRATCH5
+	mfspr	r9, SPRN_SPRG_SCRATCH5
 	mfspr	r11, SPRN_SPRG_SCRATCH6
-	mtspr	SPRN_PID, r12
+	mtspr	SPRN_PID, r9
 	mtcr	r11
 	mfspr	r9, SPRN_SPRG_SCRATCH4
 	mfspr	r12, SPRN_SPRG_SCRATCH3
@@ -343,9 +342,9 @@ _ENTRY(saved_ksp_limit)
 	mtspr	SPRN_SPRG_SCRATCH3, r12
 	mtspr	SPRN_SPRG_SCRATCH4, r9
 	mfcr	r11
-	mfspr	r12, SPRN_PID
+	mfspr	r9, SPRN_PID
 	mtspr	SPRN_SPRG_SCRATCH6, r11
-	mtspr	SPRN_SPRG_SCRATCH5, r12
+	mtspr	SPRN_SPRG_SCRATCH5, r9
 	mfspr	r10, SPRN_SRR0		/* Get faulting address */
 
 	/* If we are faulting a kernel address, we have to use the
@@ -368,12 +367,12 @@ _ENTRY(saved_ksp_limit)
 4:
 	tophys(r11, r11)
 	rlwimi	r11, r10, 12, 20, 29	/* Create L1 (pgdir/pmd) address */
-	lwz	r12, 0(r11)		/* Get L1 entry */
-	andi.	r9, r12, _PMD_PRESENT	/* Check if it points to a PTE page */
+	lwz	r11, 0(r11)		/* Get L1 entry */
+	andi.	r9, r11, _PMD_PRESENT	/* Check if it points to a PTE page */
 	beq	2f			/* Bail if no table */
 
-	rlwimi	r12, r10, 22, 20, 29	/* Compute PTE address */
-	lwz	r11, 0(r12)		/* Get Linux PTE */
+	rlwimi	r11, r10, 22, 20, 29	/* Compute PTE address */
+	lwz	r11, 0(r11)		/* Get Linux PTE */
 #ifdef CONFIG_SWAP
 	li	r9, _PAGE_PRESENT | _PAGE_ACCESSED | _PAGE_EXEC
 #else
@@ -389,13 +388,13 @@ _ENTRY(saved_ksp_limit)
 	/* Create TLB tag.  This is the faulting address plus a static
 	 * set of bits.  These are size, valid, E, U0.
 	*/
-	li	r12, 0x00c0
-	rlwimi	r10, r12, 0, 20, 31
+	li	r9, 0x00c0
+	rlwimi	r10, r9, 0, 20, 31
 
 	b	finish_tlb_load
 
 2:	/* Check for possible large-page pmd entry */
-	rlwinm.	r9, r12, 2, 22, 24
+	rlwinm.	r9, r11, 2, 22, 24
 	beq	5f
 
 	/* Create TLB tag.  This is the faulting address, plus a static
@@ -403,7 +402,6 @@ _ENTRY(saved_ksp_limit)
 	 */
 	ori	r9, r9, 0x40
 	rlwimi	r10, r9, 0, 20, 31
-	mr	r11, r12
 
 	b	finish_tlb_load
 
@@ -411,9 +409,9 @@ _ENTRY(saved_ksp_limit)
 	/* The bailout.  Restore registers to pre-exception conditions
 	 * and call the heavyweights to help us out.
 	 */
-	mfspr	r12, SPRN_SPRG_SCRATCH5
+	mfspr	r9, SPRN_SPRG_SCRATCH5
 	mfspr	r11, SPRN_SPRG_SCRATCH6
-	mtspr	SPRN_PID, r12
+	mtspr	SPRN_PID, r9
 	mtcr	r11
 	mfspr	r9, SPRN_SPRG_SCRATCH4
 	mfspr	r12, SPRN_SPRG_SCRATCH3
@@ -529,7 +527,7 @@ WDTException:
 	 * miss get to this point to load the TLB.
 	 * 	r10 - TLB_TAG value
 	 * 	r11 - Linux PTE
-	 *	r12, r9 - available to use
+	 *	r9 - available to use
 	 *	PID - loaded with proper value when we get here
 	 *	Upon exit, we reload everything and RFI.
 	 * Actually, it will fit now, but oh well.....a common place
@@ -538,30 +536,28 @@ WDTException:
 tlb_4xx_index:
 	.long	0
 finish_tlb_load:
-	/* load the next available TLB index.
-	*/
-	lwz	r9, tlb_4xx_index@l(0)
-	addi	r9, r9, 1
-	andi.	r9, r9, (PPC40X_TLB_SIZE-1)
-	stw	r9, tlb_4xx_index@l(0)
-
-6:
 	/*
 	 * Clear out the software-only bits in the PTE to generate the
 	 * TLB_DATA value.  These are the bottom 2 bits of the RPM, the
 	 * top 3 bits of the zone field, and M.
 	 */
-	li	r12, 0x0ce2
-	andc	r11, r11, r12
+	li	r9, 0x0ce2
+	andc	r11, r11, r9
+
+	/* load the next available TLB index. */
+	lwz	r9, tlb_4xx_index@l(0)
+	addi	r9, r9, 1
+	andi.	r9, r9, PPC40X_TLB_SIZE - 1
+	stw	r9, tlb_4xx_index@l(0)
 
 	tlbwe	r11, r9, TLB_DATA		/* Load TLB LO */
 	tlbwe	r10, r9, TLB_TAG		/* Load TLB HI */
 
 	/* Done...restore registers and get out of here.
 	*/
-	mfspr	r12, SPRN_SPRG_SCRATCH5
+	mfspr	r9, SPRN_SPRG_SCRATCH5
 	mfspr	r11, SPRN_SPRG_SCRATCH6
-	mtspr	SPRN_PID, r12
+	mtspr	SPRN_PID, r9
 	mtcr	r11
 	mfspr	r9, SPRN_SPRG_SCRATCH4
 	mfspr	r12, SPRN_SPRG_SCRATCH3