powerpc/8xx: Use SPRN_SPRG_SCRATCH2 in DTLB miss exception

Use SPRN_SPRG_SCRATCH2 in DTLB miss exception instead of DAR
in order to be similar to ITLB miss exception.

This also simplifies mpc8xx_pmu_del()
Signed-off-by: Christophe Leroy <christophe.leroy@csgroup.eu>
Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>
Link: https://lore.kernel.org/r/e3cc8f023ef40e1e8ae144e4dd1330a5ff022528.1606231483.git.christophe.leroy@csgroup.eu

arch/powerpc/kernel/head_8xx.S

@@ -247,7 +247,7 @@ InstructionTLBMiss:
 
 	. = 0x1200
 DataStoreTLBMiss:
-	mtspr	SPRN_DAR, r10
+	mtspr	SPRN_SPRG_SCRATCH2, r10
 	mtspr	SPRN_M_TW, r11
 	mfcr	r11
 
@@ -286,11 +286,11 @@ DataStoreTLBMiss:
 	li	r11, RPN_PATTERN
 	rlwimi	r10, r11, 0, 24, 27	/* Set 24-27 */
 	mtspr	SPRN_MD_RPN, r10	/* Update TLB entry */
+	mtspr	SPRN_DAR, r11		/* Tag DAR */
 
 	/* Restore registers */
 
-0:	mfspr	r10, SPRN_DAR
-	mtspr	SPRN_DAR, r11	/* Tag DAR */
+0:	mfspr	r10, SPRN_SPRG_SCRATCH2
 	mfspr	r11, SPRN_M_TW
 	rfi
 	patch_site	0b, patch__dtlbmiss_exit_1
@@ -300,8 +300,7 @@ DataStoreTLBMiss:
 0:	lwz	r10, (dtlb_miss_counter - PAGE_OFFSET)@l(0)
 	addi	r10, r10, 1
 	stw	r10, (dtlb_miss_counter - PAGE_OFFSET)@l(0)
-	mfspr	r10, SPRN_DAR
-	mtspr	SPRN_DAR, r11	/* Tag DAR */
+	mfspr	r10, SPRN_SPRG_SCRATCH2
 	mfspr	r11, SPRN_M_TW
 	rfi
 #endif

arch/powerpc/perf/8xx-pmu.c

@@ -153,6 +153,11 @@ static void mpc8xx_pmu_read(struct perf_event *event)
 
 static void mpc8xx_pmu_del(struct perf_event *event, int flags)
 {
+	struct ppc_inst insn;
+
+	/* mfspr r10, SPRN_SPRG_SCRATCH2 */
+	insn = ppc_inst(PPC_INST_MFSPR | __PPC_RS(R10) | __PPC_SPR(SPRN_SPRG_SCRATCH2));
+
 	mpc8xx_pmu_read(event);
 
 	/* If it was the last user, stop counting to avoid useles overhead */
@@ -164,22 +169,12 @@ static void mpc8xx_pmu_del(struct perf_event *event, int flags)
 			mtspr(SPRN_ICTRL, 7);
 		break;
 	case PERF_8xx_ID_ITLB_LOAD_MISS:
-		if (atomic_dec_return(&itlb_miss_ref) == 0) {
-			/* mfspr r10, SPRN_SPRG_SCRATCH2 */
-			struct ppc_inst insn = ppc_inst(PPC_INST_MFSPR | __PPC_RS(R10) |
-					    __PPC_SPR(SPRN_SPRG_SCRATCH2));
-
+		if (atomic_dec_return(&itlb_miss_ref) == 0)
 			patch_instruction_site(&patch__itlbmiss_exit_1, insn);
-		}
 		break;
 	case PERF_8xx_ID_DTLB_LOAD_MISS:
-		if (atomic_dec_return(&dtlb_miss_ref) == 0) {
-			/* mfspr r10, SPRN_DAR */
-			struct ppc_inst insn = ppc_inst(PPC_INST_MFSPR | __PPC_RS(R10) |
-					    __PPC_SPR(SPRN_DAR));
-
+		if (atomic_dec_return(&dtlb_miss_ref) == 0)
 			patch_instruction_site(&patch__dtlbmiss_exit_1, insn);
-		}
 		break;
 	}
 }