powerpc: Use SWITCH_FRAME_SIZE for prom and rtas entry

Commit 6c1719942e19 ("powerpc/of: Remove useless register save/restore
when calling OF back") removed the saving of srr0 and srr1 when calling
into OpenFirmware. Commit e31aa453bbc4 ("powerpc: Use LOAD_REG_IMMEDIATE
only for constants on 64-bit") did the same for rtas.

This means we don't need to save the extra stack space and can use
the common SWITCH_FRAME_SIZE.

There were already no users of _SRR0 and _SRR1 so we can remove them
too.

Link: https://github.com/linuxppc/linux/issues/83
Signed-off-by: Joel Stanley <joel@jms.id.au>
Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>

arch/powerpc/kernel/asm-offsets.c

@@ -280,11 +280,6 @@ int main(void)
 	/* Interrupt register frame */
 	DEFINE(INT_FRAME_SIZE, STACK_INT_FRAME_SIZE);
 	DEFINE(SWITCH_FRAME_SIZE, STACK_FRAME_OVERHEAD + sizeof(struct pt_regs));
-#ifdef CONFIG_PPC64
-	/* Create extra stack space for SRR0 and SRR1 when calling prom/rtas. */
-	DEFINE(PROM_FRAME_SIZE, STACK_FRAME_OVERHEAD + sizeof(struct pt_regs) + 16);
-	DEFINE(RTAS_FRAME_SIZE, STACK_FRAME_OVERHEAD + sizeof(struct pt_regs) + 16);
-#endif /* CONFIG_PPC64 */
 	STACK_PT_REGS_OFFSET(GPR0, gpr[0]);
 	STACK_PT_REGS_OFFSET(GPR1, gpr[1]);
 	STACK_PT_REGS_OFFSET(GPR2, gpr[2]);
@@ -328,10 +323,6 @@ int main(void)
 	STACK_PT_REGS_OFFSET(_ESR, dsisr);
 #else /* CONFIG_PPC64 */
 	STACK_PT_REGS_OFFSET(SOFTE, softe);
-
-	/* These _only_ to be used with {PROM,RTAS}_FRAME_SIZE!!! */
-	DEFINE(_SRR0, STACK_FRAME_OVERHEAD+sizeof(struct pt_regs));
-	DEFINE(_SRR1, STACK_FRAME_OVERHEAD+sizeof(struct pt_regs)+8);
 #endif /* CONFIG_PPC64 */
 
 #if defined(CONFIG_PPC32)

arch/powerpc/kernel/entry_64.S

@@ -1124,7 +1124,7 @@ _ASM_NOKPROBE_SYMBOL(fast_exception_return);
 _GLOBAL(enter_rtas)
 	mflr	r0
 	std	r0,16(r1)
-        stdu	r1,-RTAS_FRAME_SIZE(r1)	/* Save SP and create stack space. */
+        stdu	r1,-SWITCH_FRAME_SIZE(r1) /* Save SP and create stack space. */
 
 	/* Because RTAS is running in 32b mode, it clobbers the high order half
 	 * of all registers that it saves.  We therefore save those registers
@@ -1256,7 +1256,7 @@ rtas_restore_regs:
 	ld	r8,_DSISR(r1)
 	mtdsisr	r8
 
-        addi	r1,r1,RTAS_FRAME_SIZE	/* Unstack our frame */
+        addi	r1,r1,SWITCH_FRAME_SIZE	/* Unstack our frame */
 	ld	r0,16(r1)		/* get return address */
 
 	mtlr    r0
@@ -1267,7 +1267,7 @@ rtas_restore_regs:
 _GLOBAL(enter_prom)
 	mflr	r0
 	std	r0,16(r1)
-        stdu	r1,-PROM_FRAME_SIZE(r1)	/* Save SP and create stack space */
+        stdu	r1,-SWITCH_FRAME_SIZE(r1) /* Save SP and create stack space */
 
 	/* Because PROM is running in 32b mode, it clobbers the high order half
 	 * of all registers that it saves.  We therefore save those registers
@@ -1324,8 +1324,8 @@ _GLOBAL(enter_prom)
 	REST_10GPRS(22, r1)
 	ld	r4,_CCR(r1)
 	mtcr	r4
-	
-        addi	r1,r1,PROM_FRAME_SIZE
+
+        addi	r1,r1,SWITCH_FRAME_SIZE
 	ld	r0,16(r1)
 	mtlr    r0
         blr