powerpc: Use names rather than numbers for SPRGs (v2)

The kernel uses SPRG registers for various purposes, typically in
low level assembly code as scratch registers or to hold per-cpu
global infos such as the PACA or the current thread_info pointer.

We want to be able to easily shuffle the usage of those registers
as some implementations have specific constraints realted to some
of them, for example, some have userspace readable aliases, etc..
and the current choice isn't always the best.

This patch should not change any code generation, and replaces the
usage of SPRN_SPRGn everywhere in the kernel with a named replacement
and adds documentation next to the definition of the names as to
what those are used for on each processor family.

The only parts that still use the original numbers are bits of KVM
or suspend/resume code that just blindly needs to save/restore all
the SPRGs.

Signed-off-by: Benjamin Herrenschmidt <benh@kernel.crashing.org>

1 files changed, 16 insertions, 28 deletions

diff --git a/arch/powerpc/kernel/exceptions-64s.S b/arch/powerpc/kernel/exceptions-64s.S
index 72644cf22cac..4e9640cc0563 100644
--- a/arch/powerpc/kernel/exceptions-64s.S
+++ b/arch/powerpc/kernel/exceptions-64s.S
@@ -24,18 +24,6 @@
  * 0x8000 -        : Early init and support code
  */
 
-
-/*
- *   SPRG Usage
- *
- *   Register	Definition
- *
- *   SPRG0	reserved for hypervisor
- *   SPRG1	temp - used to save gpr
- *   SPRG2	temp - used to save gpr
- *   SPRG3	virt addr of paca
- */
-
 /*
  * This is the start of the interrupt handlers for pSeries
  * This code runs with relocation off.
@@ -53,16 +41,16 @@ __start_interrupts:
 	. = 0x200
 _machine_check_pSeries:
 	HMT_MEDIUM
-	mtspr	SPRN_SPRG1,r13		/* save r13 */
+	mtspr	SPRN_SPRG_SCRATCH0,r13		/* save r13 */
 	EXCEPTION_PROLOG_PSERIES(PACA_EXMC, machine_check_common)
 
 	. = 0x300
 	.globl data_access_pSeries
 data_access_pSeries:
 	HMT_MEDIUM
-	mtspr	SPRN_SPRG1,r13
+	mtspr	SPRN_SPRG_SCRATCH0,r13
 BEGIN_FTR_SECTION
-	mtspr	SPRN_SPRG2,r12
+	mtspr	SPRN_SPRG_SCRATCH1,r12
 	mfspr	r13,SPRN_DAR
 	mfspr	r12,SPRN_DSISR
 	srdi	r13,r13,60
@@ -71,7 +59,7 @@ BEGIN_FTR_SECTION
 	cmpwi	r13,0x2c
 	beq	do_stab_bolted_pSeries
 	mtcrf	0x80,r12
-	mfspr	r12,SPRN_SPRG2
+	mfspr	r12,SPRN_SPRG_SCRATCH1
 END_FTR_SECTION_IFCLR(CPU_FTR_SLB)
 	EXCEPTION_PROLOG_PSERIES(PACA_EXGEN, data_access_common)
 
@@ -79,8 +67,8 @@ END_FTR_SECTION_IFCLR(CPU_FTR_SLB)
 	.globl data_access_slb_pSeries
 data_access_slb_pSeries:
 	HMT_MEDIUM
-	mtspr	SPRN_SPRG1,r13
-	mfspr	r13,SPRN_SPRG3		/* get paca address into r13 */
+	mtspr	SPRN_SPRG_SCRATCH0,r13
+	mfspr	r13,SPRN_SPRG_PACA		/* get paca address into r13 */
 	std	r3,PACA_EXSLB+EX_R3(r13)
 	mfspr	r3,SPRN_DAR
 	std	r9,PACA_EXSLB+EX_R9(r13)	/* save r9 - r12 */
@@ -93,7 +81,7 @@ data_access_slb_pSeries:
 	std	r10,PACA_EXSLB+EX_R10(r13)
 	std	r11,PACA_EXSLB+EX_R11(r13)
 	std	r12,PACA_EXSLB+EX_R12(r13)
-	mfspr	r10,SPRN_SPRG1
+	mfspr	r10,SPRN_SPRG_SCRATCH0
 	std	r10,PACA_EXSLB+EX_R13(r13)
 	mfspr	r12,SPRN_SRR1		/* and SRR1 */
 #ifndef CONFIG_RELOCATABLE
@@ -117,8 +105,8 @@ data_access_slb_pSeries:
 	.globl instruction_access_slb_pSeries
 instruction_access_slb_pSeries:
 	HMT_MEDIUM
-	mtspr	SPRN_SPRG1,r13
-	mfspr	r13,SPRN_SPRG3		/* get paca address into r13 */
+	mtspr	SPRN_SPRG_SCRATCH0,r13
+	mfspr	r13,SPRN_SPRG_PACA		/* get paca address into r13 */
 	std	r3,PACA_EXSLB+EX_R3(r13)
 	mfspr	r3,SPRN_SRR0		/* SRR0 is faulting address */
 	std	r9,PACA_EXSLB+EX_R9(r13)	/* save r9 - r12 */
@@ -131,7 +119,7 @@ instruction_access_slb_pSeries:
 	std	r10,PACA_EXSLB+EX_R10(r13)
 	std	r11,PACA_EXSLB+EX_R11(r13)
 	std	r12,PACA_EXSLB+EX_R12(r13)
-	mfspr	r10,SPRN_SPRG1
+	mfspr	r10,SPRN_SPRG_SCRATCH0
 	std	r10,PACA_EXSLB+EX_R13(r13)
 	mfspr	r12,SPRN_SRR1		/* and SRR1 */
 #ifndef CONFIG_RELOCATABLE
@@ -161,7 +149,7 @@ BEGIN_FTR_SECTION
 	beq-	1f
 END_FTR_SECTION_IFSET(CPU_FTR_REAL_LE)
 	mr	r9,r13
-	mfspr	r13,SPRN_SPRG3
+	mfspr	r13,SPRN_SPRG_PACA
 	mfspr	r11,SPRN_SRR0
 	ld	r12,PACAKBASE(r13)
 	ld	r10,PACAKMSR(r13)
@@ -230,14 +218,14 @@ masked_interrupt:
 	rotldi	r10,r10,16
 	mtspr	SPRN_SRR1,r10
 	ld	r10,PACA_EXGEN+EX_R10(r13)
-	mfspr	r13,SPRN_SPRG1
+	mfspr	r13,SPRN_SPRG_SCRATCH0
 	rfid
 	b	.
 
 	.align	7
 do_stab_bolted_pSeries:
 	mtcrf	0x80,r12
-	mfspr	r12,SPRN_SPRG2
+	mfspr	r12,SPRN_SPRG_SCRATCH1
 	EXCEPTION_PROLOG_PSERIES(PACA_EXSLB, .do_stab_bolted)
 
 #ifdef CONFIG_PPC_PSERIES
@@ -248,14 +236,14 @@ do_stab_bolted_pSeries:
       .align 7
 system_reset_fwnmi:
 	HMT_MEDIUM
-	mtspr	SPRN_SPRG1,r13		/* save r13 */
+	mtspr	SPRN_SPRG_SCRATCH0,r13		/* save r13 */
 	EXCEPTION_PROLOG_PSERIES(PACA_EXGEN, system_reset_common)
 
 	.globl machine_check_fwnmi
       .align 7
 machine_check_fwnmi:
 	HMT_MEDIUM
-	mtspr	SPRN_SPRG1,r13		/* save r13 */
+	mtspr	SPRN_SPRG_SCRATCH0,r13		/* save r13 */
 	EXCEPTION_PROLOG_PSERIES(PACA_EXMC, machine_check_common)
 
 #endif /* CONFIG_PPC_PSERIES */
@@ -270,7 +258,7 @@ slb_miss_user_pseries:
 	std	r10,PACA_EXGEN+EX_R10(r13)
 	std	r11,PACA_EXGEN+EX_R11(r13)
 	std	r12,PACA_EXGEN+EX_R12(r13)
-	mfspr	r10,SPRG1
+	mfspr	r10,SPRG_SCRATCH0
 	ld	r11,PACA_EXSLB+EX_R9(r13)
 	ld	r12,PACA_EXSLB+EX_R3(r13)
 	std	r10,PACA_EXGEN+EX_R13(r13)