powerpc/8xx: Use SCRATCH0 and SCRATCH1 also for TLB handlers

SCRATCH0 and SCRATCH1 are only used in Exceptions prologs where no other
exception can happen. There is therefore no need to preserve them accross
TLB handlers, we can use them there as in other exceptions. One of the
advantages is that they do not suffer CPU6 errata unlike M_TW register.
Signed-off-by: Christophe Leroy <christophe.leroy@c-s.fr>
Signed-off-by: Scott Wood <scottwood@freescale.com>

arch/powerpc/kernel/head_8xx.S

@@ -104,12 +104,15 @@ turn_on_mmu:
  * task's thread_struct.
  */
 #define EXCEPTION_PROLOG	\
-	mtspr	SPRN_SPRG_SCRATCH0,r10;	\
-	mtspr	SPRN_SPRG_SCRATCH1,r11;	\
-	mfcr	r10;		\
+	EXCEPTION_PROLOG_0;	\
 	EXCEPTION_PROLOG_1;	\
 	EXCEPTION_PROLOG_2
 
+#define EXCEPTION_PROLOG_0	\
+	mtspr	SPRN_SPRG_SCRATCH0,r10;	\
+	mtspr	SPRN_SPRG_SCRATCH1,r11;	\
+	mfcr	r10
+
 #define EXCEPTION_PROLOG_1	\
 	mfspr	r11,SPRN_SRR1;		/* check whether user or kernel */ \
 	andi.	r11,r11,MSR_PR;	\
@@ -144,6 +147,14 @@ turn_on_mmu:
 	SAVE_4GPRS(3, r11);	\
 	SAVE_2GPRS(7, r11)
 
+/*
+ * Exception exit code.
+ */
+#define EXCEPTION_EPILOG_0	\
+	mtcr	r10;		\
+	mfspr	r10,SPRN_SPRG_SCRATCH0;	\
+	mfspr	r11,SPRN_SPRG_SCRATCH1
+
 /*
  * Note: code which follows this uses cr0.eq (set if from kernel),
  * r11, r12 (SRR0), and r9 (SRR1).
@@ -293,16 +304,8 @@ InstructionTLBMiss:
 #ifdef CONFIG_8xx_CPU6
 	stw	r3, 8(r0)
 #endif
-	DO_8xx_CPU6(0x3f80, r3)
-	mtspr	SPRN_M_TW, r10	/* Save a couple of working registers */
-	mfcr	r10
-#ifdef CONFIG_8xx_CPU6
-	stw	r10, 0(r0)
-	stw	r11, 4(r0)
-#else
-	mtspr	SPRN_DAR, r10
-	mtspr	SPRN_SPRG_SCRATCH2, r11
-#endif
+	EXCEPTION_PROLOG_0
+	mtspr	SPRN_SPRG_SCRATCH2, r10
 	mfspr	r10, SPRN_SRR0	/* Get effective address of fault */
 #ifdef CONFIG_8xx_CPU15
 	addi	r11, r10, 0x1000
@@ -359,18 +362,11 @@ InstructionTLBMiss:
 	mtspr	SPRN_MI_RPN, r10	/* Update TLB entry */
 
 	/* Restore registers */
-#ifndef CONFIG_8xx_CPU6
-	mfspr	r10, SPRN_DAR
-	mtcr	r10
-	mtspr	SPRN_DAR, r11	/* Tag DAR */
-	mfspr	r11, SPRN_SPRG_SCRATCH2
-#else
-	lwz	r11, 0(r0)
-	mtcr	r11
-	lwz	r11, 4(r0)
+#ifdef CONFIG_8xx_CPU6
 	lwz	r3, 8(r0)
 #endif
-	mfspr	r10, SPRN_M_TW
+	mfspr	r10, SPRN_SPRG_SCRATCH2
+	EXCEPTION_EPILOG_0
 	rfi
 2:
 	mfspr	r11, SPRN_SRR1
@@ -381,19 +377,11 @@ InstructionTLBMiss:
 	mtspr	SPRN_SRR1, r11
 
 	/* Restore registers */
-#ifndef CONFIG_8xx_CPU6
-	mfspr	r10, SPRN_DAR
-	mtcr	r10
-	li	r11, 0x00f0
-	mtspr	SPRN_DAR, r11	/* Tag DAR */
-	mfspr	r11, SPRN_SPRG_SCRATCH2
-#else
-	lwz	r11, 0(r0)
-	mtcr	r11
-	lwz	r11, 4(r0)
+#ifdef CONFIG_8xx_CPU6
 	lwz	r3, 8(r0)
 #endif
-	mfspr	r10, SPRN_M_TW
+	mfspr	r10, SPRN_SPRG_SCRATCH2
+	EXCEPTION_EPILOG_0
 	b	InstructionAccess
 
 	. = 0x1200
@@ -401,16 +389,8 @@ DataStoreTLBMiss:
 #ifdef CONFIG_8xx_CPU6
 	stw	r3, 8(r0)
 #endif
-	DO_8xx_CPU6(0x3f80, r3)
-	mtspr	SPRN_M_TW, r10	/* Save a couple of working registers */
-	mfcr	r10
-#ifdef CONFIG_8xx_CPU6
-	stw	r10, 0(r0)
-	stw	r11, 4(r0)
-#else
-	mtspr	SPRN_DAR, r10
-	mtspr	SPRN_SPRG_SCRATCH2, r11
-#endif
+	EXCEPTION_PROLOG_0
+	mtspr	SPRN_SPRG_SCRATCH2, r10
 	mfspr	r10, SPRN_M_TWB	/* Get level 1 table entry address */
 
 	/* If we are faulting a kernel address, we have to use the
@@ -483,19 +463,12 @@ DataStoreTLBMiss:
 	mtspr	SPRN_MD_RPN, r10	/* Update TLB entry */
 
 	/* Restore registers */
-#ifndef CONFIG_8xx_CPU6
-	mfspr	r10, SPRN_DAR
-	mtcr	r10
-	mtspr	SPRN_DAR, r11	/* Tag DAR */
-	mfspr	r11, SPRN_SPRG_SCRATCH2
-#else
-	mtspr	SPRN_DAR, r11	/* Tag DAR */
-	lwz	r11, 0(r0)
-	mtcr	r11
-	lwz	r11, 4(r0)
+#ifdef CONFIG_8xx_CPU6
 	lwz	r3, 8(r0)
 #endif
-	mfspr	r10, SPRN_M_TW
+	mtspr	SPRN_DAR, r11	/* Tag DAR */
+	mfspr	r10, SPRN_SPRG_SCRATCH2
+	EXCEPTION_EPILOG_0
 	rfi
 
 /* This is an instruction TLB error on the MPC8xx.  This could be due
@@ -519,23 +492,18 @@ DataTLBError:
 #ifdef CONFIG_8xx_CPU6
 	stw	r3, 8(r0)
 #endif
-	DO_8xx_CPU6(0x3f80, r3)
-	mtspr	SPRN_M_TW, r10	/* Save a couple of working registers */
-	mfcr	r10
-	stw	r10, 0(r0)
-	stw	r11, 4(r0)
+	EXCEPTION_PROLOG_0
+	mtspr	SPRN_SPRG_SCRATCH2, r10
 
 	mfspr	r10, SPRN_DAR
 	cmpwi	cr0, r10, 0x00f0
 	beq-	FixupDAR	/* must be a buggy dcbX, icbi insn. */
 DARFixed:/* Return from dcbx instruction bug workaround, r10 holds value of DAR */
-	mfspr	r10, SPRN_M_TW	/* Restore registers */
-	lwz	r11, 0(r0)
-	mtcr	r11
-	lwz	r11, 4(r0)
 #ifdef CONFIG_8xx_CPU6
 	lwz	r3, 8(r0)
 #endif
+	mfspr	r10,SPRN_SPRG_SCRATCH2
+	EXCEPTION_EPILOG_0
 	b	DataAccess
 
 	EXCEPTION(0x1500, Trap_15, unknown_exception, EXC_XFER_EE)
@@ -619,8 +587,8 @@ FixupDAR:/* Entry point for dcbx workaround. */
 	stw	r11,0(r10)	/* store add/and instruction */
 	dcbf	0,r10		/* flush new instr. to memory. */
 	icbi	0,r10		/* invalidate instr. cache line */
-	lwz	r11, 4(r0)	/* restore r11 from memory */
-	mfspr	r10, SPRN_M_TW	/* restore r10 from M_TW */
+	mfspr	r11, SPRN_SPRG_SCRATCH1	/* restore r11 */
+	mfspr	r10, SPRN_SPRG_SCRATCH0	/* restore r10 */
 	isync			/* Wait until new instr is loaded from memory */
 modified_instr:
 	.space	4		/* this is where the add instr. is stored */
@@ -683,9 +651,9 @@ modified_instr:
 	b	DARFixed		/* Go back to normal TLB handling */
 
 	/* special handling for r10,r11 since these are modified already */
-153:	lwz	r11, 4(r0)	/* load r11 from memory */
+153:	mfspr	r11, SPRN_SPRG_SCRATCH1	/* load r11 from SPRN_SPRG_SCRATCH1 */
 	b	155f
-154:	mfspr	r11, SPRN_M_TW	/* load r10 from M_TW */
+154:	mfspr	r11, SPRN_SPRG_SCRATCH0	/* load r10 from SPRN_SPRG_SCRATCH0 */
 155:	add	r10, r10, r11	/* add it */
 	mfctr	r11		/* restore r11 */
 	b	151b