ARM: pm: allow suspend finisher to return error codes

There are SoCs where attempting to enter a low power state is ignored,
and the CPU continues executing instructions with all state preserved.
It is over-complex at that point to disable the MMU just to call the
resume path.

Instead, allow the suspend finisher to return error codes to abort
suspend in this circumstance, where the cpu_suspend internals will then
unwind the saved state on the stack.  Also omit the tlb flush as no
changes to the page tables will have happened.

Signed-off-by: Russell King <rmk+kernel@arm.linux.org.uk>

arch/arm/kernel/sleep.S

@@ -12,7 +12,6 @@
  *  r1 = v:p offset
  *  r2 = suspend function arg0
  *  r3 = suspend function
- * Note: does not return until system resumes
  */
 ENTRY(__cpu_suspend)
 	stmfd	sp!, {r4 - r11, lr}
@@ -26,7 +25,7 @@ ENTRY(__cpu_suspend)
 #endif
 	mov	r6, sp			@ current virtual SP
 	sub	sp, sp, r5		@ allocate CPU state on stack
-	mov	r0, sp			@ save pointer
+	mov	r0, sp			@ save pointer to CPU save block
 	add	ip, ip, r1		@ convert resume fn to phys
 	stmfd	sp!, {r1, r6, ip}	@ save v:p, virt SP, phys resume fn
 	ldr	r5, =sleep_save_sp
@@ -55,10 +54,17 @@ ENTRY(__cpu_suspend)
 #else
 	bl	__cpuc_flush_kern_all
 #endif
+	adr	lr, BSYM(cpu_suspend_abort)
 	ldmfd	sp!, {r0, pc}		@ call suspend fn
 ENDPROC(__cpu_suspend)
 	.ltorg
 
+cpu_suspend_abort:
+	ldmia	sp!, {r1 - r3}		@ pop v:p, virt SP, phys resume fn
+	mov	sp, r2
+	ldmfd	sp!, {r4 - r11, pc}
+ENDPROC(cpu_suspend_abort)
+
 /*
  * r0 = control register value
  * r1 = v:p offset (preserved by cpu_do_resume)
@@ -89,6 +95,7 @@ cpu_resume_after_mmu:
 	str	r5, [r2, r4, lsl #2]	@ restore old mapping
 	mcr	p15, 0, r0, c1, c0, 0	@ turn on D-cache
 	bl	cpu_init		@ restore the und/abt/irq banked regs
+	mov	r0, #0			@ return zero on success
 	ldmfd	sp!, {r4 - r11, pc}
 ENDPROC(cpu_resume_after_mmu)