ARC: boot: Support Halt-on-reset and Run-on-reset SMP booting modes

For Run-on-reset, non masters need to spin wait. For Halt-on-reset they
can jump to entry point directly.

Also while at it, made reset vector handler as "the" entry point for
kernel including host debugger based boot (which uses the ELF header
entry point)

Signed-off-by: Vineet Gupta <vgupta@synopsys.com>

arch/arc/Kconfig

@@ -194,6 +194,16 @@ config NR_CPUS
 	range 2 4096
 	default "4"
 
+config ARC_SMP_HALT_ON_RESET
+	bool "Enable Halt-on-reset boot mode"
+	default y if ARC_UBOOT_SUPPORT
+	help
+	  In SMP configuration cores can be configured as Halt-on-reset
+	  or they could all start at same time. For Halt-on-reset, non
+	  masters are parked until Master kicks them so they can start of
+	  at designated entry point. For other case, all jump to common
+	  entry point and spin wait for Master's signal.
+
 endif	#SMP
 
 menuconfig ARC_CACHE

arch/arc/kernel/entry-arcv2.S

@@ -24,7 +24,7 @@
 	.align 4
 
 # Initial 16 slots are Exception Vectors
-VECTOR	stext			; Restart Vector (jump to entry point)
+VECTOR	res_service		; Reset Vector
 VECTOR	mem_service		; Mem exception
 VECTOR	instr_service		; Instrn Error
 VECTOR	EV_MachineCheck		; Fatal Machine check

arch/arc/kernel/entry-compact.S

@@ -86,7 +86,7 @@
  */
 
 ; ********* Critical System Events **********************
-VECTOR   res_service             ; 0x0, Restart Vector  (0x0)
+VECTOR   res_service             ; 0x0, Reset Vector	(0x0)
 VECTOR   mem_service             ; 0x8, Mem exception   (0x1)
 VECTOR   instr_service           ; 0x10, Instrn Error   (0x2)
 
@@ -155,13 +155,9 @@ int2_saved_reg:
 ; ---------------------------------------------
 	.section .text, "ax",@progbits
 
-res_service:		; processor restart
-	flag    0x1     ; not implemented
-	nop
-	nop
 
-reserved:		; processor restart
-	rtie            ; jump to processor initializations
+reserved:
+	flag 1		; Unexpected event, halt
 
 ;##################### Interrupt Handling ##############################
 

arch/arc/kernel/head.S

@@ -50,28 +50,37 @@
 .endm
 
 	.section .init.text, "ax",@progbits
-	.type stext, @function
-	.globl stext
-stext:
-	;-------------------------------------------------------------------
-	; Don't clobber r0-r2 yet. It might have bootloader provided info
-	;-------------------------------------------------------------------
+
+;----------------------------------------------------------------
+; Default Reset Handler (jumped into from Reset vector)
+; - Don't clobber r0,r1,r2 as they might have u-boot provided args
+; - Platforms can override this weak version if needed
+;----------------------------------------------------------------
+WEAK(res_service)
+	j	stext
+END(res_service)
+
+;----------------------------------------------------------------
+; Kernel Entry point
+;----------------------------------------------------------------
+ENTRY(stext)
 
 	CPU_EARLY_SETUP
 
 #ifdef CONFIG_SMP
-	; Ensure Boot (Master) proceeds. Others wait in platform dependent way
-	;	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
-	mov.ne	r0, r5
-	jne	arc_platform_smp_wait_to_boot
+	mov.nz	r0, r5
+#ifdef CONFIG_ARC_SMP_HALT_ON_RESET
+	; Non-Master can proceed as system would be booted sufficiently
+	jnz	first_lines_of_secondary
+#else
+	; Non-Masters wait for Master to boot enough and bring them up
+	jnz	arc_platform_smp_wait_to_boot
+#endif
+	; Master falls thru
 #endif
+
 	; Clear BSS before updating any globals
 	; XXX: use ZOL here
 	mov	r5, __bss_start
@@ -102,16 +111,14 @@ stext:
 	GET_TSK_STACK_BASE r9, sp	; r9 = tsk, sp = stack base(output)
 
 	j	start_kernel	; "C" entry point
+END(stext)
 
 #ifdef CONFIG_SMP
 ;----------------------------------------------------------------
 ;     First lines of code run by secondary before jumping to 'C'
 ;----------------------------------------------------------------
 	.section .text, "ax",@progbits
-	.type first_lines_of_secondary, @function
-	.globl first_lines_of_secondary
-
-first_lines_of_secondary:
+ENTRY(first_lines_of_secondary)
 
 	CPU_EARLY_SETUP
 
@@ -126,5 +133,5 @@ first_lines_of_secondary:
 	GET_TSK_STACK_BASE r0, sp
 
 	j	start_kernel_secondary
-
+END(first_lines_of_secondary)
 #endif

arch/arc/kernel/vmlinux.lds.S

@@ -12,7 +12,7 @@
 #include <asm/thread_info.h>
 
 OUTPUT_ARCH(arc)
-ENTRY(_stext)
+ENTRY(res_service)
 
 #ifdef CONFIG_CPU_BIG_ENDIAN
 jiffies = jiffies_64 + 4;