m68knommu: ColdFire add support for kernel preemption

As the subject says this patch adds the support for kernel preemption
on m68knommu Coldfire. I thing the same changes could be applied to
68360 & 68328 but since I don't have the HW for testing, I don't touch it.
Signed-off-by: Sebastian Siewior <bigeasy@linutronix.de>
Signed-off-by: Greg Ungerer <gerg@uclinux.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

arch/m68knommu/kernel/asm-offsets.c

@@ -87,6 +87,7 @@ int main(void)
 	DEFINE(TI_TASK, offsetof(struct thread_info, task));
 	DEFINE(TI_EXECDOMAIN, offsetof(struct thread_info, exec_domain));
 	DEFINE(TI_FLAGS, offsetof(struct thread_info, flags));
+	DEFINE(TI_PREEMPTCOUNT, offsetof(struct thread_info, preempt_count));
 	DEFINE(TI_CPU, offsetof(struct thread_info, cpu));
 
 	return 0;

arch/m68knommu/platform/coldfire/entry.S

@@ -106,6 +106,22 @@ ret_from_exception:
 	btst	#5,%sp@(PT_SR)		/* check if returning to kernel */
 	jeq	Luser_return		/* if so, skip resched, signals */
 
+#ifdef CONFIG_PREEMPT
+	movel	%sp,%d1			/* get thread_info pointer */
+	andl	#-THREAD_SIZE,%d1	/* at base of kernel stack */
+	movel	%d1,%a0
+	movel	%a0@(TI_FLAGS),%d1	/* get thread_info->flags */
+	andl	#_TIF_NEED_RESCHED,%d1
+	jeq	Lkernel_return
+
+	movel	%a0@(TI_PREEMPTCOUNT),%d1
+	cmpl	#0,%d1
+	jne	Lkernel_return
+
+	pea	Lkernel_return
+	jmp	preempt_schedule_irq	/* preempt the kernel */
+#endif
+
 Lkernel_return:
 	moveml	%sp@,%d1-%d5/%a0-%a2
 	lea	%sp@(32),%sp		/* space for 8 regs */