powerpc: Enable the Watchdog vector for 405

The watchdog and FIT code has been #if 0'd for ever, if the CPU takes
an exception to either of those vectors it will jump into the middle
of the PIT or Data TLB code and surely crash.

At least some (all?) 405 cores have both the WDT and FIT
vectors defined, so lets have proper entry points for them.

Tested that the WDT vector works on a 405F6 core.
Signed-off-by: Jason Gunthorpe <jgunthorpe@obsidianresearch.com>
Signed-off-by: Benjamin Herrenschmidt <benh@kernel.crashing.org>

arch/powerpc/kernel/head_40x.S

@@ -430,30 +430,18 @@ label:
 	EXCEPTION(0x0F00, Trap_0F, unknown_exception, EXC_XFER_EE)
 
 /* 0x1000 - Programmable Interval Timer (PIT) Exception */
-	START_EXCEPTION(0x1000, Decrementer)
-	NORMAL_EXCEPTION_PROLOG
-	lis	r0,TSR_PIS@h
-	mtspr	SPRN_TSR,r0		/* Clear the PIT exception */
-	addi	r3,r1,STACK_FRAME_OVERHEAD
-	EXC_XFER_LITE(0x1000, timer_interrupt)
-
-#if 0
-/* NOTE:
- * FIT and WDT handlers are not implemented yet.
- */
+	. = 0x1000
+	b Decrementer
 
 /* 0x1010 - Fixed Interval Timer (FIT) Exception
 */
-	STND_EXCEPTION(0x1010,	FITException,		unknown_exception)
+	. = 0x1010
+	b FITException
 
 /* 0x1020 - Watchdog Timer (WDT) Exception
 */
-#ifdef CONFIG_BOOKE_WDT
-	CRITICAL_EXCEPTION(0x1020, WDTException, WatchdogException)
-#else
-	CRITICAL_EXCEPTION(0x1020, WDTException, unknown_exception)
-#endif
-#endif
+	. = 0x1020
+	b WDTException
 
 /* 0x1100 - Data TLB Miss Exception
  * As the name implies, translation is not in the MMU, so search the
@@ -738,6 +726,29 @@ label:
 		(MSR_KERNEL & ~(MSR_ME|MSR_DE|MSR_CE)), \
 		NOCOPY, crit_transfer_to_handler, ret_from_crit_exc)
 
+	/* Programmable Interval Timer (PIT) Exception. (from 0x1000) */
+Decrementer:
+	NORMAL_EXCEPTION_PROLOG
+	lis	r0,TSR_PIS@h
+	mtspr	SPRN_TSR,r0		/* Clear the PIT exception */
+	addi	r3,r1,STACK_FRAME_OVERHEAD
+	EXC_XFER_LITE(0x1000, timer_interrupt)
+
+	/* Fixed Interval Timer (FIT) Exception. (from 0x1010) */
+FITException:
+	NORMAL_EXCEPTION_PROLOG
+	addi	r3,r1,STACK_FRAME_OVERHEAD;
+	EXC_XFER_EE(0x1010, unknown_exception)
+
+	/* Watchdog Timer (WDT) Exception. (from 0x1020) */
+WDTException:
+	CRITICAL_EXCEPTION_PROLOG;
+	addi	r3,r1,STACK_FRAME_OVERHEAD;
+	EXC_XFER_TEMPLATE(WatchdogException, 0x1020+2,
+	                  (MSR_KERNEL & ~(MSR_ME|MSR_DE|MSR_CE)),
+			  NOCOPY, crit_transfer_to_handler,
+			  ret_from_crit_exc)
+
 /*
  * The other Data TLB exceptions bail out to this point
  * if they can't resolve the lightweight TLB fault.

arch/powerpc/kernel/traps.c

@@ -1515,7 +1515,7 @@ void unrecoverable_exception(struct pt_regs *regs)
 	die("Unrecoverable exception", regs, SIGABRT);
 }
 
-#ifdef CONFIG_BOOKE_WDT
+#if defined(CONFIG_BOOKE_WDT) || defined(CONFIG_40x)
 /*
  * Default handler for a Watchdog exception,
  * spins until a reboot occurs