ARC: SMP failed to boot due to missing IVT setup

Commit 05b016ecf5e7a "ARC: Setup Vector Table Base in early boot" moved
the Interrupt vector Table setup out of arc_init_IRQ() which is called
for all CPUs, to entry point of boot cpu only, breaking booting of others.

Fix by adding the same to entry point of non-boot CPUs too.

read_arc_build_cfg_regs() printing IVT Base Register didn't help the
casue since it prints a synthetic value if zero which is totally bogus,
so fix that to print the exact Register.

[vgupta: Remove the now stale comment from header of arc_init_IRQ and
also added the commentary for halt-on-reset]

Cc: Gilad Ben-Yossef <[e-mail]>
Cc: Cc: <[e-mail]> #3.11
Signed-off-by: Noam Camus <[e-mail]>
Signed-off-by: Vineet Gupta <[e-mail]>
Signed-off-by: Linus Torvalds <[e-mail]>

arch/arc/include/asm/sections.h

···
 
 #include <asm-generic/sections.h>
 
-extern char _int_vec_base_lds[];
 extern char __arc_dccm_base[];
 extern char __dtb_start[];
 

arch/arc/kernel/head.S

···
 	;	IDENTITY Reg [ 3  2  1  0 ]
 	;	(cpu-id)             ^^^	=> Zero for UP ARC700
 	;					=> #Core-ID if SMP (Master 0)
+	; Note that non-boot CPUs might not land here if halt-on-reset and
+	; instead breath life from @first_lines_of_secondary, but we still
+	; need to make sure only boot cpu takes this path.
 	GET_CPU_ID  r5
 	cmp	r5, 0
 	jnz	arc_platform_smp_wait_to_boot
···
 	.globl first_lines_of_secondary
 
 first_lines_of_secondary:
+
+	sr	@_int_vec_base_lds, [AUX_INTR_VEC_BASE]
 
 	; setup per-cpu idle task as "current" on this CPU
 	ld	r0, [@secondary_idle_tsk]

arch/arc/kernel/irq.c

···
  * -Needed for each CPU (hence not foldable into init_IRQ)
  *
  * what it does ?
- * -setup Vector Table Base Reg - in case Linux not linked at 0x8000_0000
  * -Disable all IRQs (on CPU side)
  * -Optionally, setup the High priority Interrupts as Level 2 IRQs
  */

arch/arc/kernel/setup.c

···
 	READ_BCR(AUX_IDENTITY, cpu->core);
 
 	cpu->timers = read_aux_reg(ARC_REG_TIMERS_BCR);
-
 	cpu->vec_base = read_aux_reg(AUX_INTR_VEC_BASE);
-	if (cpu->vec_base == 0)
-		cpu->vec_base = (unsigned int)_int_vec_base_lds;
 
 	READ_BCR(ARC_REG_D_UNCACH_BCR, uncached_space);
 	cpu->uncached_base = uncached_space.start << 24;