parisc: enable wide mode early

The idle task might have been allocated above 4GB. With the current code
we cannot access that memory because the CPU is still running in narrow
mode.
This was found on a J5000 machine and the patch is required to enable
SPARSEMEM on that machine.
Signed-off-by: NSven Schnelle <svens@stackframe.org>
Signed-off-by: NHelge Deller <deller@gmx.de>

arch/parisc/kernel/head.S

@@ -329,6 +329,19 @@ smp_slave_stext:
 	mtsp	   %r0,%sr6
 	mtsp	   %r0,%sr7
 
+#ifdef CONFIG_64BIT
+	/*
+	 *  Enable Wide mode early, in case the task_struct for the idle
+	 *  task in smp_init_current_idle_task was allocated above 4GB.
+	 */
+1:	mfia            %rp             /* clear upper part of pcoq */
+	ldo             2f-1b(%rp),%rp
+	depdi           0,31,32,%rp
+	bv              (%rp)
+	ssm             PSW_SM_W,%r0
+2:
+#endif
+
 	/*  Initialize the SP - monarch sets up smp_init_current_idle_task */
 	load32		PA(smp_init_current_idle_task),%sp
 	LDREG		0(%sp),%sp	/* load task address */