MIPS: microMIPS: Add support for exception handling.

All exceptions must be taken in microMIPS mode, never in classic
MIPS mode or the kernel falls apart. A few NOP instructions are
used to maintain the correct alignment of microMIPS versions of
the exception vectors.

Signed-off-by: Steven J. Hill <Steven.Hill@imgtec.com>

arch/mips/kernel/genex.S

@@ -5,8 +5,8 @@
  *
  * Copyright (C) 1994 - 2000, 2001, 2003 Ralf Baechle
  * Copyright (C) 1999, 2000 Silicon Graphics, Inc.
- * Copyright (C) 2001 MIPS Technologies, Inc.
  * Copyright (C) 2002, 2007  Maciej W. Rozycki
+ * Copyright (C) 2001, 2012 MIPS Technologies, Inc.  All rights reserved.
  */
 #include <linux/init.h>
 
@@ -21,8 +21,10 @@
 #include <asm/war.h>
 #include <asm/thread_info.h>
 
+#ifdef CONFIG_MIPS_MT_SMTC
 #define PANIC_PIC(msg)					\
-		.set push;				\
+		.set	push;				\
+		.set	nomicromips;			\
 		.set	reorder;			\
 		PTR_LA	a0,8f;				\
 		.set	noat;				\
@@ -31,17 +33,10 @@
 9:		b	9b;				\
 		.set	pop;				\
 		TEXT(msg)
+#endif
 
 	__INIT
 
-NESTED(except_vec0_generic, 0, sp)
-	PANIC_PIC("Exception vector 0 called")
-	END(except_vec0_generic)
-
-NESTED(except_vec1_generic, 0, sp)
-	PANIC_PIC("Exception vector 1 called")
-	END(except_vec1_generic)
-
 /*
  * General exception vector for all other CPUs.
  *
@@ -138,12 +133,19 @@ LEAF(r4k_wait)
 	 nop
 	nop
 	nop
+#ifdef CONFIG_CPU_MICROMIPS
+	nop
+	nop
+	nop
+	nop
+#endif
 	.set	mips3
 	wait
 	/* end of rollback region (the region size must be power of two) */
-	.set	pop
 1:
 	jr	ra
+	nop
+	.set	pop
 	END(r4k_wait)
 
 	.macro	BUILD_ROLLBACK_PROLOGUE handler
@@ -201,7 +203,11 @@ NESTED(handle_int, PT_SIZE, sp)
 	LONG_L	s0, TI_REGS($28)
 	LONG_S	sp, TI_REGS($28)
 	PTR_LA	ra, ret_from_irq
-	j	plat_irq_dispatch
+	PTR_LA  v0, plat_irq_dispatch
+	jr	v0
+#ifdef CONFIG_CPU_MICROMIPS
+	nop
+#endif
 	END(handle_int)
 
 	__INIT
@@ -222,11 +228,14 @@ NESTED(except_vec4, 0, sp)
 /*
  * EJTAG debug exception handler.
  * The EJTAG debug exception entry point is 0xbfc00480, which
- * normally is in the boot PROM, so the boot PROM must do a
+ * normally is in the boot PROM, so the boot PROM must do an
  * unconditional jump to this vector.
  */
 NESTED(except_vec_ejtag_debug, 0, sp)
 	j	ejtag_debug_handler
+#ifdef CONFIG_CPU_MICROMIPS
+	 nop
+#endif
 	END(except_vec_ejtag_debug)
 
 	__FINIT
@@ -251,9 +260,10 @@ NESTED(except_vec_vi, 0, sp)
 FEXPORT(except_vec_vi_mori)
 	ori	a0, $0, 0
 #endif /* CONFIG_MIPS_MT_SMTC */
+	PTR_LA	v1, except_vec_vi_handler
 FEXPORT(except_vec_vi_lui)
 	lui	v0, 0		/* Patched */
-	j	except_vec_vi_handler
+	jr	v1
 FEXPORT(except_vec_vi_ori)
 	 ori	v0, 0		/* Patched */
 	.set	pop
@@ -354,6 +364,9 @@ EXPORT(ejtag_debug_buffer)
  */
 NESTED(except_vec_nmi, 0, sp)
 	j	nmi_handler
+#ifdef CONFIG_CPU_MICROMIPS
+	 nop
+#endif
 	END(except_vec_nmi)
 
 	__FINIT
@@ -500,13 +513,35 @@ NESTED(nmi_handler, PT_SIZE, sp)
 	.set	push
 	.set	noat
 	.set	noreorder
-	/* 0x7c03e83b: rdhwr v1,$29 */
+	/* MIPS32:    0x7c03e83b: rdhwr v1,$29 */
+	/* microMIPS: 0x007d6b3c: rdhwr v1,$29 */
 	MFC0	k1, CP0_EPC
-	lui	k0, 0x7c03
-	lw	k1, (k1)
-	ori	k0, 0xe83b
-	.set	reorder
+#if defined(CONFIG_CPU_MICROMIPS) || defined(CONFIG_CPU_MIPS32_R2) || defined(CONFIG_CPU_MIPS64_R2)
+	and     k0, k1, 1
+	beqz    k0, 1f
+	xor     k1, k0
+	lhu     k0, (k1)
+	lhu     k1, 2(k1)
+	ins     k1, k0, 16, 16
+	lui     k0, 0x007d
+	b       docheck
+	ori     k0, 0x6b3c
+1:
+	lui     k0, 0x7c03
+	lw      k1, (k1)
+	ori     k0, 0xe83b
+#else
+	andi    k0, k1, 1
+	bnez    k0, handle_ri
+	lui     k0, 0x7c03
+	lw      k1, (k1)
+	ori     k0, 0xe83b
+#endif
+	.set    reorder
+docheck:
 	bne	k0, k1, handle_ri	/* if not ours */
+
+isrdhwr:
 	/* The insn is rdhwr.  No need to check CAUSE.BD here. */
 	get_saved_sp	/* k1 := current_thread_info */
 	.set	noreorder