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, 7 insertions, 7 deletions

diff --git a/arch/powerpc/kernel/head_64.S b/arch/powerpc/kernel/head_64.S
index 9196ef36d433..0552f01041ab 100644
--- a/arch/powerpc/kernel/head_64.S
+++ b/arch/powerpc/kernel/head_64.S
@@ -195,7 +195,7 @@ _GLOBAL(generic_secondary_smp_init)
 	mr	r3,r24			/* not found, copy phys to r3	 */
 	b	.kexec_wait		/* next kernel might do better	 */
 
-2:	mtspr	SPRN_SPRG3,r13		/* Save vaddr of paca in SPRG3	 */
+2:	mtspr	SPRN_SPRG_PACA,r13	/* Save vaddr of paca in an SPRG */
 	/* From now on, r24 is expected to be logical cpuid */
 	mr	r24,r5
 3:	HMT_LOW
@@ -484,7 +484,7 @@ _GLOBAL(pmac_secondary_start)
 	LOAD_REG_ADDR(r4,paca)		/* Get base vaddr of paca array	*/
 	mulli	r13,r24,PACA_SIZE	/* Calculate vaddr of right paca */
 	add	r13,r13,r4		/* for this processor.		*/
-	mtspr	SPRN_SPRG3,r13		/* Save vaddr of paca in SPRG3	*/
+	mtspr	SPRN_SPRG_PACA,r13	/* Save vaddr of paca in an SPRG*/
 
 	/* Create a temp kernel stack for use before relocation is on.	*/
 	ld	r1,PACAEMERGSP(r13)
@@ -502,10 +502,10 @@ _GLOBAL(pmac_secondary_start)
  *   1. Processor number
  *   2. Segment table pointer (virtual address)
  * On entry the following are set:
- *   r1	= stack pointer.  vaddr for iSeries, raddr (temp stack) for pSeries
- *   r24   = cpu# (in Linux terms)
- *   r13   = paca virtual address
- *   SPRG3 = paca virtual address
+ *   r1	       = stack pointer.  vaddr for iSeries, raddr (temp stack) for pSeries
+ *   r24       = cpu# (in Linux terms)
+ *   r13       = paca virtual address
+ *   SPRG_PACA = paca virtual address
  */
 	.globl	__secondary_start
 __secondary_start:
@@ -641,7 +641,7 @@ _INIT_STATIC(start_here_multiplatform)
 
 	/* Restore parameters passed from prom_init/kexec */
 	mr	r3,r31
-	bl	.early_setup		/* also sets r13 and SPRG3 */
+	bl	.early_setup		/* also sets r13 and SPRG_PACA */
 
 	LOAD_REG_ADDR(r3, .start_here_common)
 	ld	r4,PACAKMSR(r13)