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)