powerpc: Use LOAD_REG_IMMEDIATE only for constants on 64-bit

Using LOAD_REG_IMMEDIATE to get the address of kernel symbols
generates 5 instructions where LOAD_REG_ADDR can do it in one,
and will generate R_PPC64_ADDR16_* relocations in the output when
we get to making the kernel as a position-independent executable,
which we'd rather not have to handle.  This changes various bits
of assembly code to use LOAD_REG_ADDR when we need to get the
address of a symbol, or to use suitable position-independent code
for cases where we can't access the TOC for various reasons, or
if we're not running at the address we were linked at.

It also cleans up a few minor things; there's no reason to save and
restore SRR0/1 around RTAS calls, __mmu_off can get the return
address from LR more conveniently than the caller can supply it in
R4 (and we already assume elsewhere that EA == RA if the MMU is on
in early boot), and enable_64b_mode was using 5 instructions where
2 would do.

Signed-off-by: Paul Mackerras <paulus@samba.org>

arch/powerpc/include/asm/ppc_asm.h

@@ -268,7 +268,7 @@ GLUE(.,name):
  *   Loads the value of the constant expression 'expr' into register 'rn'
  *   using immediate instructions only.  Use this when it's important not
  *   to reference other data (i.e. on ppc64 when the TOC pointer is not
- *   valid).
+ *   valid) and when 'expr' is a constant or absolute address.
  *
  * LOAD_REG_ADDR(rn, name)
  *   Loads the address of label 'name' into register 'rn'.  Use this when

arch/powerpc/kernel/cpu_setup_ppc970.S

@@ -110,7 +110,7 @@ load_hids:
 	isync
 
 	/* Save away cpu state */
-	LOAD_REG_IMMEDIATE(r5,cpu_state_storage)
+	LOAD_REG_ADDR(r5,cpu_state_storage)
 
 	/* Save HID0,1,4 and 5 */
 	mfspr	r3,SPRN_HID0
@@ -134,7 +134,7 @@ _GLOBAL(__restore_cpu_ppc970)
 	rldicl.	r0,r0,4,63
 	beqlr
 
-	LOAD_REG_IMMEDIATE(r5,cpu_state_storage)
+	LOAD_REG_ADDR(r5,cpu_state_storage)
 	/* Before accessing memory, we make sure rm_ci is clear */
 	li	r0,0
 	mfspr	r3,SPRN_HID4

arch/powerpc/kernel/entry_64.S

@@ -690,10 +690,6 @@ _GLOBAL(enter_rtas)
 	std	r7,_DAR(r1)
 	mfdsisr	r8
 	std	r8,_DSISR(r1)
-	mfsrr0	r9
-	std	r9,_SRR0(r1)
-	mfsrr1	r10
-	std	r10,_SRR1(r1)
 
 	/* Temporary workaround to clear CR until RTAS can be modified to
 	 * ignore all bits.
@@ -754,21 +750,27 @@ _STATIC(rtas_return_loc)
 	mfspr	r4,SPRN_SPRG3	        /* Get PACA */
 	clrldi	r4,r4,2			/* convert to realmode address */
 
+	bcl	20,31,$+4
+0:	mflr	r3
+	ld	r3,(1f-0b)(r3)		/* get &.rtas_restore_regs */
+
 	mfmsr   r6
 	li	r0,MSR_RI
 	andc	r6,r6,r0
 	sync	
 	mtmsrd  r6
 
         ld	r1,PACAR1(r4)           /* Restore our SP */
-	LOAD_REG_IMMEDIATE(r3,.rtas_restore_regs)
         ld	r4,PACASAVEDMSR(r4)     /* Restore our MSR */
 
 	mtspr	SPRN_SRR0,r3
 	mtspr	SPRN_SRR1,r4
 	rfid
 	b	.	/* prevent speculative execution */
 
+	.align	3
+1:	.llong	.rtas_restore_regs
+
 _STATIC(rtas_restore_regs)
 	/* relocation is on at this point */
 	REST_GPR(2, r1)			/* Restore the TOC */
@@ -788,10 +790,6 @@ _STATIC(rtas_restore_regs)
 	mtdar	r7
 	ld	r8,_DSISR(r1)
 	mtdsisr	r8
-	ld	r9,_SRR0(r1)
-	mtsrr0	r9
-	ld	r10,_SRR1(r1)
-	mtsrr1	r10
 
         addi	r1,r1,RTAS_FRAME_SIZE	/* Unstack our frame */
 	ld	r0,16(r1)		/* get return address */